Simple Bat Detector Amplifier
Tony Messina - Las Vegas, NV
One question that always seems to come up is : How do I hook up a speaker to the Simple Bat Detector ?
The first thing I usually explain is that the amplification levels of the Simple Bat Detector are so high that it really becomes impractical to put a speaker in the same case as the detector. If you did you would have too much feedback and oscillation from the transducer and speaker being too close together. You could reduce the gain of the detector ... but then you wouldn't be able to hear bats unless they were very close.
So, what can you do ? Many times I also want to share the bat calls with small groups of people, so I know how handy a speaker can be. What I do, and what I suggest to others, is to use a battery powered amplified speaker. Some examples of these are shown below ...
The amplified speaker on the left is home-made ... more on that in a bit ... The other two were sold by Radio Shack in the past. ( There is an item similar to the middle speaker in the current Radio Shack catalog at about $13 - p/n 2062620 ). The amplifier on the right was designed as a telephone amplifier, and normally uses a telephone pickup coil on a cable that plugs in at the back of the unit.
All of these amplifiers have three things in common ... They have mono 3.5mm input plugs - like the one used on the Simple Bat Detector, they run on a single 9 volt battery, and they have a volume control.
To use this type of amplifier you simply connect it to the Simple Bat Detector with a 6 foot cable that has 3.5mm mono plugs at both ends ( like the one in the picture above ). Then you point the detector at the bats, and position the amplified speaker for the best listening of the group.
Building an Amplified Speaker...
|OK ... I've convinced you to use a separate amplified
speaker ... but you would like to follow a do-it-yourself
approach - like you did for the detector. Well, that
turns out to be rather easy to do.
The amplified speaker to the left is a perfect compliment to the Simple Bat Detector, and is relatively easy to construct for the electronics hobbiest.
I simply got one of the many 386 amplifier kits available on the market, and wired it up in a case like the one used for the Simple Bat Detector - along with a speaker and a volume control knob
|In the picture to the right you can see the general
approach needed to wire up a 386 module.
The volume control is wired to the spot on the PCB where a PCB pot was supposed to have gone.
The switch is used to select either a gain of 20 or 200 by wiring it to the spot on the PCB where the gain resistor would have been. ( You can omit this option )
I don't have a power switch as I have used the input jack to control the power in the same way as I have with the earphone jack in the Simple Bat Detector
The amplifier module I used in this case is one that only has the 386 amplifier chip ... no preamp ... and sells for less than $5 at MPJA as part number 6017KT. The case and input jack are the same type used in the Simple Bat Detector, and the battery clip is included with the case. All that is left to acquire is an 8 ohm speaker, volume control, and some wire to hook it all up. The cost of all the parts will be around $20, so you won't save anything over the cost of the commercially available amplifier ... but you will be able to say you made it yourself :-)
Tony Messina - Las Vegas, Nevada - email: T-Rex@ix.netcom.com