API Monitor - Handbook V1

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Copyright P. Zimmermann 2010 Page 1

The Apimonitor

(Acoustic Hive Monitor)Version 1.0.

Copyright Notice:

Copyright P Zimmermann 2010.

This document may be copied, printed and freely distributed on condition that no changes

are made to the text and no charge is made either for distribution or reproduction.

Reproductions of this document must be accompanied by acknowledgement of the source

of the original data.


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CONTENTS

1 Introduction

2 Design Philosophy

3 Outline definition

4 The Electronics - A Bit More Detail5 Operating Instructions

6 Maintenance / Testing

7 Notes For The Experimenter

8 Appendix

Copyright Notice:

Copyright P Zimmermann 2010.

This document may be copied, printed and freely distributed on condition that no changes are

made to the text and no charge is made either for distribution or reproduction. Reproductions of

this document must be accompanied by acknowledgement of the source of the original data.


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1.0. Introduction;

The Apimonitor has been developed in response to an apparent demand for an up to date

and reproducible means of determining activity within the bee colony, specifically the

precursory activity to swarming.

The link between acoustic activity and colony swarming has been known for a number of

years and a great deal of work was carried out by the late Eddie Woods, who not only

proved the link but made many measurements of the frequencies produced, and by

carrying out these measurements on active hives was able to demonstrate the correlation

between the two. The measurement data was predictable enough for Eddie to produce his

own device which he called the Apidictor. This device used early transistor technology

and was produced in small numbers in the early 60s.

A more detailed description of Eddies work can be found at the following website

http://beedata.com/data2/listen/listenbees.htm

It must be emphasized that the Apimonitor described within this document is not a copyof the original Apidictor, it is instead a measurement device, that will allow a beekeeper

to monitor the sounds within the hive and with practice to be able to predict the onset of

swarming. To this end, the Apimonitor has been developed with filters of similar

frequencies to those used in the original Apidictor. However, due to the differences in

component technologies and the lack of hard data regarding the performance of the

original Apidictor, the performance of the Apimonitor will invariably be different and the

need for practice along with detailed hive observation will still be paramount for

successful operation. I make no claims as to the originality of any of the circuitry

published here. So, look upon the Apimonitor as a tool to listen with and to assist with

making judgements based on your own observations of hive activity and bee behaviour.

The Apimonitor may well work sufficiently well to be of use in the intended manner,however, I suspect that it will benefit from additional testing which will need to be carried

out along with observations of bee activity, which may in the long term lead to better /

different filter characteristics and gains. As such, the design presented within this

document should be viewed as a starting point and will not give a yes / no answer to

the questions Are my bees about to swarm? or Has my queen gone AWOL?

As I do not have the time and facilities to do in depth testing and measuring in the field as

it were, I am presenting this design as an open source design, into the public domain. You

are welcome and indeed encouraged to copy it / modify it as you see fit with the proviso

that all information, drawings etc are copied along with appropriate acknowledgements of

the source of the original data. I would very much welcome feedback from any one who

has a chance to try out this design along with any modifications or changes that may

result.


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2.0. The Design Philosophy:The design presented here was conceived as a result of an apparent need for an up to date

acoustic hive monitor. However, before proceeding with the design, there were several

ground rules, which had to be established first. These helped to keep track of theoriginal requirement and are listed below in no particular order:-

2.1. Keep things as simple as possible.

2.2. Keep it as cost effective as possible.

2.3. We are not trying to re-invent the wheel here so we wont try stick to well

proven principles and technology.

2.4. As well as being able to listen to the sounds within the hive, a basic relative

measure of sound level would be highly desirable.

2.5. We will be using a microphone to measure airborne sounds within the hive. It is

not the intention to measure sound vibration through contact with the hive

structure; although this may be an alternative approach should someone else

choose to pursue it.The measuring microphone is to be small, rugged and cheap for ease of

replacement. The environment within the hive is not a benign one and the

microphone may well get damaged or propolised!

2.6. The complete unit is to be portable and battery powered.

2.7. Means shall be provided to enable connection of a secondary monitor /

recording device.

2.8. Avoid exotic components, industry standard components are to be used

wherever possible. This will make DIY build, component sourcing and repair

much easier.

This set of ground rules although not exhaustive, already eliminates certain options and

defines the bones of our design.

In addition, with particular reference to 2.3. above, we already know the following about

Eddie Woods Apidictor:-

There were 3 switch settings:

Switch position 1 provided an All Pass function with no filtering.

Switch position 2 provided a Band Pass function to listen to thewarble.

Switch position 3 was a High Pass function to listen to the hiss.

An indicator was provided for the measurement of relative level.


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To add a bit more detail to some of these original functions, a brief description of each as

I understand them follows:

The All Pass function is basically an amplifier with a flat response. There is no

deliberate attempt to apply filtering to the microphone signal, so what the microphonepicks up is what we hear. (Subject to the limitations of the microphone and the vagaries of

the human ear of course!)

The Band Pass function allows a predefined narrow range of frequencies through to the

indicator and headphones. Frequencies above and below this narrow band are

progressively attenuated (reduced). Various sources state that the original Apidictor band

pass filter had a pass band of 225 to 285Hz and as we have no reason to change it, we

will stick with something similar. The function of the Band pass filter is to isolate the

warbling sound that the bees make from general background noise and thus make it

more readily audible and therefore measureable. What is debatable though is the

sharpness or selectivity of the filter. I have seen several different sources of graphs

purporting to be measurements of the Apidictor filter response, but no firm evidence tosupport this. Unfortunately, the filter response has a direct effect on any measurements

made so the selectivity or Q of the filter is fundamental to the unit performance. For

the moment we will adhere to the time honoured method of the first order guesstimate.

Most analogue filters are inevitably compromises and this one will be no different. The

filter ultimately will be a balance of effectiveness, simplicity, stability and cost whilst at

the same time adhering to the original frequency requirements as much as possible.

The High Pass function is basically an amplifier that allows more of a signal to pass as

the frequency increases. Thus it provides a rising response where the amplitude (loudness)

of the signal rises as the frequency or pitch of the signal increases. The function of the

High Pass filter is to enable us to listen to the high pitched hiss that bees make under

certain conditions. The original Apidictor had a filter with a 3kHz corner frequency,which we will also retain for our own design. Dont worry too much about the filter

terminology here, more detailed explanations will follow later.

Finally the last key item was an indicator. The Apidictor used a magic eye, which was in

common use at the time. It was a special variant of the vacuum valve but is now outdated

technology and not suitable for a portable, low power approach. We will retain an

indicator but it will operate in a slightly different manner and will be more suitable for a

low cost portable item.


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3.0. Outline Definition:

We now have some limited visibility of our basic design and can now identify the main

functional blocks that need our attention.

Microphone: Small, rugged and cheap pretty much defines the modern electret

microphone. They are to be found in all sorts of equipment from portable stereos, karaoke

machines, car alarms to telephones. They are available as noise cancelling types which

will reject a certain amount of background noise but in this application I dont think that

will be an overriding requirement. In contrast to a moving coil microphone, an electret

microphone needs power to be able to function. Most common or garden electrets willwork with any supply voltage in the range of 1.5 volts to 10 volts Ideal for our battery

powered unit.

Indicator: Moving coil meters are relatively expensive items these days and if you are

gutting an old piece of equipment then it may well be suitable with a bit of tweaking of

the circuit. However, I am going to assume that anyone intending to buy or build one of

these units will be keeping a careful eye on the costs and so the meter will not be included

in this design. What we will use however is a LED (light emitting diode). These are

extremely common cheap and rugged and by combining with a judicious bit of circuitry

can be made to suit our purpose here quite well.

Headphones: Again in order to keep the costs down, I am assuming that most people will

have access to a cheap pair of MP3 type stereo headphones. These are normally of 32

ohm impedance (sometimes higher) and we will use them in mono mode. Higher

impedance headphones, if you have them will probably be ok, but if you have low

impedance (


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Recorder Output: As previously mentioned, a facility to be able to connect an external

recording device is to be included. This could be a cassette recorder, solid state recorder

or a computer sound card. The output level will be appropriate for any of these that utilize

a line input. This feature will enable recorded sounds to be analysed at leisure away from

the hive.

From the preceding list of requirements a design was commenced culminating in the

schematic shown in the appendix.

The schematic is presented here for those of you who are interested or want to modify the

unit to suit your own particular needs.

If you dont understand electronics or are just not interested then skip the next section and

concentrate on the operating instructions.


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4.0. The Electronics - A Bit More Detail:This section describes each section of the Apimonitor design in a bit more detail for those

of you who are either interested or want to take things a bit further and carry out

modifications / changes of your own. The complete schematic can be found in the

appendix and the following sections will detail the operation of the various functionalblocks. Skip to section 5.0. if electronics doesnt interest you.

4.1. Microphone:

This is a rather fundamental part of the Apimonitor. It is a key item and the successful

performance or otherwise of the Apimonitor will be directly proportional to the

performance of the microphone. Rubbish in = Rubbish out!

Care should be taken if you intend using an alternative type. The microphone selected for

use in this application is a fairly typical, small and rugged electret microphone. The data

sheet for the chosen microphone can be found in the appendix. Its main features that are

useful here are:

i. Low costii. Relatively easy to obtain.

iii Physically small - it can be placed inside the hive relatively

easily, but not so small that we cant handle and solder it

easily.

iv. A flat frequency response and good sensitivity. The frequencyresponse is fairly flat over the range of frequencies that we

are interested in (approx 50Hz to 10kHz) and it is sensitive

enough that we dont need too much amplification.

The sensitivity of the microphone is specified in dBV, which is a logarithmic measure of

output voltage and usually (but not always) specified at 1 Pascal at a known or specified

distance from the sound source. The Pascal is a measure of pressure and is used to specifyacoustic sound pressure level (SPL). There are many different types of microphone on the

market that could be used but there are one or two things to bear in mind if you are

thinking of trying a different one. Firstly, to operate correctly with this circuit it must be

an electret type. This type of microphone generally has a small amplifier / buffer built into

the microphone itself and thus generally has a high sensitivity and good frequency

response. The downside however, is that it needs power to operate correctly. Modern day

computers, phones and all sorts of electronic devices use electret microphones and it is

possible to try any number of these for comparison. Just observe the correct polarity when

connecting up connecting it up back to front probably wont damage it, but it wont

work either. Do bear in mind though that a microphone of different sensitivity will give

you different results with your Apimonitor. It may or may not be significant, depending

on the difference in sensitivity and frequency response of your chosen microphone.

Do not try to connect a moving coil type of microphone to this circuit. No damage will be

caused but no or very little output will be heard. Moving coil microphones in general

have too low an output to be used without resorting to an external pre-amplifier and will

often have a frequency response that is far from flat.


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4.2. Type of Amplifier:The amplifier used in this circuit is a well-known industry standard that has been around

many years now, the TL064. It is a Low Power JFet input operational amplifier which in a

nutshell means it is well suited to low power, battery operated applications such as this.

The main features of the TL064 that we make use of are:i. Low power consumption typically 200uA per amplifier.

ii. High Gain / Bandwidth. (1MHz)iii. 4 amplifiers in one package.iv. Relatively wide operating voltage range.v. Commonly available

There are many other amplifiers that could be used in this application but as with all

things, there are trade offs and compromises. The TL064 is rather unique in that it is

specified to operate down to 6 volts and below. The TL074 / TL084 amplifiers are very

similar in performance but they will draw more power and hence battery life will be

shorter pro rata. Probably not a major issue but for long term monitoring it could be.

The OPA 4705 series from Texas are another good range with very similar performanceto the TL064. I could go on and on but there really are far too many options and

manufacturers to list them all here. The choice is yours, but use the TL064 as your

baseline for any comparisons.

4.3 The Microphone Amplifier:This stage is configured as a non-inverting,

ac-coupled amplifier. It serves to match the

microphone output to the rest of the circuitry

and also to amplify the signal up to a useable

level. The nominal mid-band gain is set to

28dB (x25).

The microphone input is applied via

capacitor C5 and resistors R6, R7 set the

overall gain. Capacitor C5 also blocks any

DC content in the input signal from reaching

the amplifier input. Resistors R10, R19 are

connected to the +9 volt supply and supply

the bias voltage needed by the electret

microphone in order for it to work correctly.


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4.4 The High Pass Filter:The amplifier shown left is the

second of four in the package U1.

Its purpose is to take the amplified

microphone signal from themicrophone amplifier above and to

apply a high pass function, which

will attenuate lower frequencies

whilst passing higher frequencies

unchanged. The transition between

the two is smooth and at a pre

determined rate of 12 dB per

octave.

This circuit configuration is known as a 2 pole filter and although it attenuates frequencies

below its corner frequency, it does not amplify above its corner frequency. The corner

frequency is set by C1, C2 and R2 and is nominally 3kHz.

4.5. The Band Pass Filter:Shown left is the band pass filter,

the function of which is to pass a

narrow pre-defined range of

frequencies and attenuate

frequencies outside this range. The

band pass function is centered on

approx. 255Hz and the sharpness or

Q of the filter is controlled by the

ratios of the components aroundU1C.

Although these types of filters can

be made adjustable, one of the

drawbacks is that the adjustments

for frequency, bandwidth and gain

are interdependant.

This stage does yield a small amount of gain of approx. 6dB (2x). No end of tweaking

could be done to the band pass filter to optimize it for the frequencies of interest.

However, this is a suggested starting point and modifications / changes are done at the

discretion of the individual.


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4.6. The All Pass Amplifier:As its name suggests, the

all pass amplifier passes all

frequencies within its pass

band essentially unchanged.This circuit configuration,

as well as inverting the

signal can also supply gain

if required. The gain is

controlled by the ratio of

resistors R8 and R9, which

in this instance fix the gain

at 0dB (or x1).

4.7 The Level Detector:The level detector

compares the input fromthe level control (R13) with

a fixed dc reference. If the

input level exceeds the

reference level the

amplifier will amplify the

difference and its output

will move positive, lighting

the LED. The greater the

signal difference, the

brighter the LED will light.

This operates as a very simple measurement function for a fixed microphone position

and sound level, the level control R13 is gradually increased (clock wise) until the LED isjust lighting. The position of the level control knob against its background scale will then

give a relative indication of signal level. Thus the louder the signal being monitored, the

lower the position of the level control knob for the LED to light. Although somewhat

crude this method avoids the use of a relatively costly and delicate meter and is fairly

intuitive to use once familiar with its operation. See the operating instructions for more

detail on this function. It should be noted that this form of level detector is supply

dependant. i.e. As the battery voltage reduces, the sensitivity of the detector will change

in proportion, but not so much as to cause a problem in use. Again, this limitation is part

of the keep it simple compromise.


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4.8 The Headphone Amplifier:The primary purpose of the

headphone amplifier is to

make the microphone output

audible to the operator of the

Apimonitor. It also serves to perform a check on the

microphone to see that it is

working correctly and is not

subject to a broken cable or

intermittent connection.

The headphone amplifier

shown above is slightly

unusual in that op-amps

arent normally used to drive

headphones, as they dont

have enough power drive capability. However, as we are only using 32 Ohm or higher

impedance headphones, we can cheat a bit. By paralleling three amplifiers, U2B, U2C andU2D their combined output is just sufficient for our purpose. This is not really

recommended practice but for our application it works well enough and keeps the costs to

a minimum. It should be noted that the headphone amplifier does not provide any voltage

gain but does provide power gain. The headphone amplifier will drive 32 Ohm or higher

MP3 type headphones but will not drive low impedance 8 Ohm types. If you require Hi

Fi quality audio, then you will be changing this stage. When using 32 Ohm type of

headphones, I would suggest you do comparative listening tests on as many different sets

as you can. They are not all created equal and some can sound quite awful.

4.9. The Line Output:

The line output circuit is alsoconnected to the selector switch,

but not to the level control. In other

words, adjustment of the level

control does not alter the output

level of the line output. However,

in common with the headphone

amplifier, it is dependant on the

setting of the selector switch. Thus

if the selector switch is set to

position 2, the line output will be the band pass filter output.

The purpose of the line output is to provide a secondary audio output of fixed level that

can be used to connect to an external recording device, a PC sound card or external

amplifier. It cannot be used for driving low impedances such as headphones or earphones.

As it has no gain adjustment control to affect it, it will always give the same output level

for a given input level i.e. repeatability for external recording will make subsequent

analysis more meaningful.


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5.0. Operating Instructions:

5.1. Position the Microphone: This may seem rather obvious but the first step israther important and so is worth spelling out. As the microphone is our window

into the acoustic world of the bee, it is important to position the microphonewithin the hive in a realistic and practical manner. This needs a bit of thought as

it needs to be done in a consistent and repeatable manner so that we can go back

and repeat measurements or make comparisons at a later stage or perhaps with a

different hive. This cannot be emphasized enough if we do not place the

microphone in the same position, we cannot be sure we are making the same

measurements or comparisons each time. That said, the bees will move around

and the colony will expand / contract over the season/s. So it is up to the bee

keeper to assess where the microphone is best located and whether it needs

moving to suit the conditions within the hive.

5.2. There is no hard and fast guaranteed correct position within a hive but the

microphone has been designed to be small enough to make locating it relativelystraight forward. Ideally the microphone once positioned should be left in place

such that the cable plug can be accessed externally and the Apimonitor

connected without disturbing the hive. This wont always be possible and will

obviously require the use of more than one microphone. Ideally each hive to be

monitored would have its own microphone or alternatively if the microphone

could be inserted or removed easily through a removable plug, then the

microphone could be used as a measurement probe and inserted as and when

required. Again bear in mind the repeatability of measurement.

5.3. The microphone is most sensitive on its end face and ideally the end face shouldface the source of the sound being measured. This isnt easy in a hive. Where is

the source of the sounds we are trying to measure? My assumption is that weneed to be monitoring the centre of the brood nest / chamber as this is where the

queen is normally to be found but there may be better locations. Time will tell.

5.4. The microphone should be located as close to the sound source as possible. Thiswill maximize the loudness of the sounds to be measured and minimize the

effects of any external / unwanted background noises.

5.5. If possible, the microphone should be located in a space between frames / combswhere there is less likelihood of the bees taking exception to it and covering it

with propolis. This is probably an impossible aim as bees will invariably trample

over the microphone, which in itself will generate noise in the microphone

signal. Any foreign object placed in a hive will generally receive the bees full

attention and eventually a good coating of propolis will ensue. Only time and

experience will determine how quickly propolis will build up and where in the

hive is to be found the best or optimum position for the microphone.


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5.6. I would recommend the fitting of an additional screen or mesh to themicrophone front face so that if propolis is a real problem the additional screen

or mesh can be easily removed and cleaned. A mesh size of 3mm or smaller

should be adequate. Alternatively the whole microphone could be mounted in or

under a mesh cover perhaps. See section 6.0.

5.7. General Monitoring: Assuming the microphone is now correctly located withinthe hive, connect a pair of 32 ohm headphones and turn on the Apimonitor, set

the selector switch to position 1 (All Pass) and increase the volume / level

control until something is audible. Depending on the level of the sounds heard,

the LED may be seen to illuminate. If nothing can be heard or very distorted

sounds are heard then try changing the battery. Switch position 1 will pass most

sounds that the bees make that we are likely to find audible. So, all being well

you will be able to hear everyday bee activity. Note: The headphone socket iswired for mono sound although you will hear it in both ears it is not true

stereo sound.

5.8. To concentrate on the warbling sound that is generally associated withswarming behaviour, set the selector switch to position 2 (Band Pass). This will

apply a narrow filter to the sounds picked up by the microphone and reduce the

level of other unwanted sounds. The centre frequency of the Band Pass filter is

around 250Hz and dependant on the level of the warbling activity, the brighter

the LED will glow as the volume or level control is advanced. Note: Whenlistening to this switch position it will sound muffled / bassy and this is entirelynormal. It is due to the attenuation of frequencies outside of the filter response.In order to make a comparison of the warbling activity on a day to day basis,

lets say that on day 1 the LED just starts to glow with a volume or level setting

of 8. Without changing the microphone location etc, on day 2 we repeat the

measurement and find the LED starts glowing with a volume or level setting of5. That means the level of warbling has increased because we have to turn

down the level or volume control to get the same brightness at the LED. In other

words, the louder the warbling, the lower the setting of the level / volume

control for the same brightness. This may seem a bit confusing and possibly

counter intuitive but think about it If there was very little in the way of

warbling i.e. a very quiet hive, then you would have to turn the level / volume

control up much higher in order to hear anything and therefore it would be a

higher setting before the LED glows if at all. With practice the beekeeper will

get a feel for what setting of the level / volume control equates to what bee

activity is being observed. This is a most important point and is the reason why

Eddie Woods spent so many years studying bee behaviour whilst at the same

time making many sound measurements.

5.9. The level detector and LED indicator have been optimized for use with the bandpass function but will however work on the other two switch settings. The High

Pass setting though, will be less sensitive. Switch setting 3 or the High Pass

setting applies a rising response filter to the microphone signal and is

optimized to listen to the hissing sound bees make if the side of the hive is

tapped. The sounds heard through the headphones in the High Pass switch


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position will sound very thin and tinny and are entirely normal and due to the

lower frequencies being heavily attenuated. As a check you can try high

frequency sounds in front of the microphone try saying Yes into the

microphone whilst emphasizing the ess. Alternatively jangle a bunch of keys

near to the microphone and you will find it very sensitive to the high frequencies

produced.

5.10. Recording / Long Term Monitoring: There may be times when you need tomonitor the hive over a longer period and maybe unattended. You may want to

record to a tape recorder, solid state recorder or to a computer in order to analyse

the sounds at your leisure, either way make sure you use a fresh battery for long

term recording. This is straight forward to do and all that is required is to

connect the line output to the line input of your chosen recording device. Be

certain to use a good quality screened lead. Temporarily connect your

headphones to the headphone socket, switch on the Apimonitor and increase the

level / volume control until you can hear hive activity. Once you are happy that

all is well, make sure the selector switch is set appropriately (see below), leave

the Apimonitor switched on, reduce the level / volume control to minimum andunplug the headphones. This will minimize the battery drain. Without the

headphones and LED operational, a theoretical battery life of around 100 hours

should be possible but this will be heavily dependant on the type of battery used.

If leaving the Apimonitor unattended at the hive, do make sure that it is

protected from the elements and is not likely to be chewed or trampled by

beasties or children.

The switch position will determine the signal present at the line output. So if you

are going to apply filtering to your recording by say using a PC and suitable

software, then set the selector switch to position 1, the All Pass function. All

frequencies picked up by the microphone will then be present in the recorded

data. If you want the recorded data to be pre-filtered then use the Band Pass or

High Pass switch positions as required.Note: Line output levels are typically in the 100 mV region and are thus too highto connect directly to a microphone input. If all you have is a microphone input,then you will need to attenuate the signal from the line output. The line outputuses a standard stereo output socket but both channels are wired to the same

source i.e. the output is 2 channel mono sound.


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6.0. Maintenance.

6.1 The MicrophoneThe microphone is probably the single most important part of the Apimonitor. It

consists of 3 main parts:

a. The electret microphone capsuleb. The connecting cablec. Connecting plug.

The microphone capsule is a small 6mm diameter electret element which is mounted

inside a small brass tube which affords additional mechanical protection and

provides electrical screening to prevent pickup of electrical noise. A resilient sleeve

covers the outside of the microphone body and also retains a small protective mesh

disc to protect the front face of the microphone. The microphone construction has

been deliberately kept simple to minimize cost and to facilitate mounting in

confined spaces. If you are using a separate mesh enclosure for the microphone, theresilient outer sleeve and mesh disc can be removed.

The connecting cable is a small diameter screened cable which connects the electret

element to the plug. The cable screen is electrically connected to the brass tube to

ensure a complete electrical screen is maintained between the electret element and

the cable plug.

The 3.5mm plug is a standard mono audio type plug and is used to connect the

microphone to the Apimonitor. Other types of pc / media type electrets can also be

connected if they are wired in the same manner, although they may give very

different results. (Tip = signal / power +ve, Outer = Gnd)

The microphone is essentially maintenance free but the following points should be

observed:

Keep the microphone dry and avoid contact with fluids. Water ingress willbe certain death for the microphone.

Keep the microphone clean and free from dust. If necessary wipe themicrophone, cable and connector with a damp cloth and allow to dry

naturally.

Do not disconnect the plug by pulling on the cable.

Keep the cable away from sharp edges / objects and avoid crushing thecable.

During use and due to its location within the hive, it is likely that the front

face of the microphone will become contaminated with propolis. This willrapidly degrade the performance of the microphone and will need to be

removed. Wipe as much off of the outer microphone surface as possible,

then gently prize the protective mesh from the front of the microphone. The

outer sleeve is resilient and the mesh can be gently eased out. Take great

care not to poke or prod the front face of the microphone with sharp

implements. The mesh can then be gently cleaned in alcohol or acetone.

When dry carefully replace the mesh back on the front of the microphone. If

propolis proves to be problematic then fit a secondary mesh to avoid


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contamination of the microphone mesh and to facilitate cleaning. In any

event it is recommended to fit a secondary mesh to afford the microphone

greater protection. It doesnt actually need to be a mesh. Any structure that

has gaps small enough to prevent bees accessing the internal face will do. So

a short tube placed over the microphone, drilled around its periphery and end

face with say 3mm holes, would probably suffice. Note: This will howevermodify the directional characteristics of the microphone.

Do not place the microphone in the hive without the protective mesh. Ifpropolis gets inside the microphone, it will be impossible to remove.

6.2. Battery: The recommended battery is a standard alkaline 9 volt PP3 (MN1604 /

6LR61) readily available from many sources. It is a non-rechargeable

type and the use of rechargeable variants is not recommended. The

battery should yield approx. 40 to 100 Hours of use but this will depend

on the operating durations / temperatures etc. If the operation of the Apimonitor is suspect, replace the battery as a

matter of course.

Always turn the Apimonitor off when not in use.

If storing the Apimonitor for extended periods always remove thebattery.

Dispose of old used batteries in a responsible manner.

6.3. The Main Apimonitor Box:Apart from keeping the main unit clean with a damp cloth, little else is needed in

the way of maintenance.

Keep the unit dry and do not immerse.

Avoid drops and sudden shocks.

Avoid extremes of temperature.

Only use the battery type recommended.


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6.4. Testing:

The Apimonitor is a relatively simple and rugged unit and as such should give

reliable service. However, if for some reason you are not sure if it is working

correctly, then there are a few simple checks that can be carried out. Check theobvious first.

If the unit appears to be completely dead, always try replacing the battery inthe first instance.

If the unit emits a continuous whistle, turn down the level control andgradually increase it to the required level. If the whistle continues, replace

the battery.

To check the microphone make sure it is plugged in to the Apimonitormicrophone socket. Plug in your headphones and switch the Apimonitor on.

Set the selector switch to position 1 (All Pass) and if you can hear sounds

picked up by the microphone then all is well. If you speak loudly into the

microphone and gradually increase the level / volume control, the LEDshould be seen to flash in sympathy with peaks in the sound level. If you

hear loud crackling when the microphone and / or cable are moved then you

have a faulty / damaged microphone cable. Replace the microphone.

Similarly if you hear pronounced humming if you handle or place your hand

near the microphone, then the cable screen is faulty. Replace the

microphone. If you hear nothing at all, then try an alternative microphone.

Assuming the microphone is working, the switch filter positions can bechecked in turn. With microphone and headphones connected, set the

selector switch to position 1 (All Pass). Switch the Apimonitor on and

position the microphone in front of a natural sound source such as a FM

radio or CD player for example. Place the microphone directly in front of

and facing the loudspeaker of the sound source. Turn up the level / volume

control until the audio can be clearly heard. It should sound natural with no

significantly enhanced or reduced frequencies. If it sounds dull or muffled,

check the microphone mesh is clean and clear of debris.

Set the selector switch to position 2 and now the audio heard in the

headphones should appear distinctly different. This is the Band Pass position

and will sound somewhat muffled with plenty of bass. Any musicians among

you can check the filter response by using the appropriate note (B3 I think)

the microphone should be quite sensitive to this note and the LED will light

dependant on the setting of the level / volume control.

Set the selector switch to position 3 (High Pass). The audio will now appear

thin and tinny. This is correct and if a set of keys is jiggled in front of themicrophone, a strong response to the high frequencies will be heard. The

LED will respond to the higher levels dependant on the setting of the level

control.


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7.0. Notes For The Experimenter:

This design has been presented as a starting point for anyone interested in taking the

research of bee / hive acoustics further. It is not and never was intended to be a complete

answer to all things acoustic and due to its simplicity and low cost some features haveeither been compromised or left out. This is the great engineering compromise where cost,

simplicity, usefulness and market all have their impact. No two engineers will give you

the same answer to this conundrum.

So where can this design be taken from here? Well how long is a piece of string? There

are many paths that lead off in different directions from here and it very much depends on

what the reader sees as priority when viewed in the context of his own personal interest.

The following discussion will expand this in a bit more detail but is by no means an

exhaustive analysis on the subject.

7.1. Application:

Although the Apimonitor has been targeted at the bee keeper, this unit could form thebasis of many other acoustic monitors, albeit with a bit of tweaking in places. There have

been suggestions of monitoring a bee hive with a vibration transducer to see what

mechanical sounds the bees produce when stomping around the hive. The present filters

within the Apimonitor could be tweaked or replaced in many ways to yield tuneable

filters that can be adjusted to suit the frequencies of interest or very narrow filters to look

at very specific frequencies. With the appropriate microphone, birdsong and other insect

sounds could be monitored. Replace the microphone with a suitable transducer and listen

to the mechanical sounds from say a car engine or the woodworm in your floorboards.

Connect it to a hydrophone and listen to the sounds produced by fish and yes they do

make noises. Im sure there are many other applications that I havent even thought of so

over to you for the ideas. What is obvious though and Eddie Woods realized all too well,

is that it is all very well measuring and recording the sounds made by different animals /insects but without detailed observation it all becomes meaningless.

7.2. The Microphone:For an acoustic monitor this is a key item and in order to make recordings where a wide

range of frequencies are going to be present, a flat response is desirable. In the appendix

the frequency response of the microphone used with the Apimonitor is shown and this is

nicely flat across the range of frequencies of interest. There are a multitude of different

microphones on the market embracing various technologies, and all coming in different

shapes and sizes. Their output characteristics and sensitivities vary widely so be careful

what you choose and study the manufacturers data carefully. The electret microphone is

probably ideally suited to the Apimonitor application, but even that could be optimized

further for sensitivity, noise cancelling, physical size etc. In recent years, silicon

microphones have become available and by use of micro machining technology are now

extremely small and quite cheap. They are not generally sealed though, so you need to

make sure they are protected from dust, the elements etc. For airborne noises microphones

are ideal. For sound transmitted in other mediums, different transducers will be required.

For vibration in a mechanical structure, vibration sensors or accelerometers will be

appropriate. For water a hydrophone or pressure transducer are the more usual sensors.


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8.0. Appendix:

Fig 1 Measured Filter Responses

Fig 2 Magnified Band Pass Filter Response

Apimonitor Ver 1.0. - Filter Responses - Measured at Line Output

-90

-80

-70

-60

-50

-40

-30

-20

100 1000 10000

Frequency (Hz)

O/PdBV

Hi Pass

Band Pass

All Pass

Apimonitor Ver 1.0. - Band Pass Filter Response - Electrical - I/P -60 dBV

-40-39

-38-37-36-35-34-33-32-31-30-29-28-27-26-25-24-23-22-21

-20

100 1000

Frequency (Hz)

O/PdBV

Band Pass

243Hz


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Fig 3 Typical Microphone Frequency Response

Fig 4 Acoustic Response Microphone to Line Output

Apimonitor Ver 1.0. - Microphone Response

-70

-65

-60

-55

-50

-45

-40

-35

-30

100 1000 10000

Frequency (Hz)

O/PdBV@9

4dBSPL(1Pa

Apimonitor Ver 1.0. - Acoustic Response

-70

-60

-50

-40

-30

-20

-10

0

100 1000 10000

Frequency (Hz)

O/PdBV


22/26


Fig 5 Apimonitor Schematic


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Fig 6 Microphone

Electret Microphone

Housing

Screened Cable

3.5mm Jack Plug (Mono)

The Apimonitor Microphone Assembly

+ TIP

SLEEVE

Electret Jack

Microphone Wiring


24/26


Fig 7 The Apimonitor Ver 1.0.


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Outline Specification (Typical values @ 9v supply):

Apimonitor V 1.0.:

Operating Voltage: 6.5 volts to 10 volts.

Supply current: 8.5 mA to include LED. (No headphone connected)

~12mA max with headphones connected.

~2.5mA No headphones, no LED.

Battery Type: MN1604 / 6LR61

Weight 160g including battery.

Frequency Response:

High Pass Filter 3kHz to >10kHz

Band Pass Filter 200Hz to 280Hz (-3dB)All Pass 10kHz

Phones 60Hz to 10kHz

Line Out 10kHz

Maximum LED Sensitivity (Typ. Measured at Microphone I/P)

All Pass 950V (-60dB) @ 1kHz

Band Pass 550V (-65dB) Typ.

High Pass 1.1mV (-59dB) Typ @ 5kHz

Microphone Connector: 3.5mm TS

Headphone Connector: 3.5mm TRS

Line Out Connector: 3.5mm TRS

Microphone:

Type Electret

Diameter 6mm

Frequency response: 20Hz to 20kHz

Sensitivity: -42dBV (3dB) (@1kHz, 1Pa)


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Fig8-MicrophoneDataSheet

Documents

API Monitor - Handbook V1