Bat Detector Prototype

[Raven Luni]

Being a total Animal lover, I always wanted to make one of these. So, I read up on the principles and looked at a few examples online.

One thing I've found with circuit examples (for pretty much anything) on the web is that they never seem to work the way people say they do, so I thought bugger it and redesigned one from scratch. It's a frequency division type and a bit of a beast in terms of component count and current draw but the prototype seems to work quite well.

So I'd like to share what I've got so far and see what people think, how it can be improved etc. One thing it lacks at the moment is a high pass filter which I'll add once I have a way to test at high frequencies. Here is the schematic:
http://www.stonewolfsoft.co.uk/temp/bd01.gif

Note that this uses the components I had available, much of which can be substituted for better / more compact versions such as replacing the flip flop ICs with a dedicated counter etc.

The amplifier was the most problematic as I had no prior experience with op amps. I tried a few single rail implementations before going split rail. I'm sure theres probably a better way to do that than that bloated splitter circuit but I wanted good stability so no expense spared there. The common base input to the counter was also the best of several attempts to get that right.

 

[Laplace]

You have this bloated rail splitter to generate a virtual ground that has no load, just the "+" LM358 inputs which draw next to zero current. Your virtual ground could easily be generated by a simple RC voltage divider instead. But you say that the LED and 7805 also draw current from the virtual ground; however, that is bad design practice since they should be referenced to physical ground instead. Also not sure why you need an 18V power supply to run the LM358 which is able to operate from much less, like 9V should be sufficient. I think I would look at replacing that common base circuit with another LM358 run from the 7805 5V power. One amp could be used for an active filter, and the other used in comparator mode to drive the clock input (use a pull-up resistor on the output of that amp).

 

[OLIVE2222]

You certainly can go for single rail and 9 volts supply.
The flip flop can directly be supplied by 9V if you swap them to CD4013 types. the 7805 as 5mA of quiescent current so better to go for a voltage divider followed by a LM358 voltage follower instead (can serve as supply for the 74HC74 too if you keep them)

 

[Raven Luni]

Thanks for the suggestions. I had been using Live Wire to simulate the thing before building it. I'd have to say that software is definitely not worth what I paid for it. One of the major problems with it is that it doesnt give you the supply pins for any logic ICs and you have to specify a standalone supply voltage. This makes it impossible to with with current from other parts of the circuit.

Anyway - since I could only simulate the preamp on its own thats probably the reason the splitter came into the picture due to the high current needed at the output. Simple voltage dividers caused all kinds of problems with swinging, oscillation etc. I'll try it out with the real circuit and let you know

One other thing though. The site I got the splitter design from (http://tangentsoft.net/elec/vgrounds.html) stated that the resistor and capacitor at the output should be 100R and 10pF respectively going no higher than 1K and 100pF. I had to take it up to 4.7K / 100pF with the real circuit to get it stable (but again that was the preamp on its own). It also said not to add capacitors at the output which I also found was very necessary.

 

[Raven Luni]

Laplace: Thanks. The extra LM358 as filter and comparator works a treat. After testing with a dog whistle the original method turned out to have a poor high frequency response. All I need to do now is add the output section to the board and I can give it to my ranger friend for some proper testing