Hello! We are hoping to trial various external ultrasonic microphones with the new AudioMoth this field season and were wondering what people have for recommendations for microphones? We will be using the devices to record bats in California. Thank you for any input!
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A while ago I suggested hooking up an SPU0410LR5H-QB with just a simple resistor to steal some power from the mic/bias pin. I have the feeling the load of the microphone is not enough and we need to create a little voltage drop in order to lower the bias voltage. Otherwise the audio might not pass through the microphone switch circuit. If you tied and found it was not working, try to add a 10k resistor over mic and gnd connection. (10k is not critical, a higher value might be a bit better for less influence on the audio)
Oh, and if I ever did sent any of you a 7mm round PCB with SPU0410LR5H-QB microphone on it, it probably has 1nF capacitors and no 1uF capacitors. 1nF creates a highpass filter effect so these only work on ultrasound. Sorry for that mistake. (8mm round versions were fine)
It would be nice to have the schematics, it looks like there is a SN74LVC1G3157 SPDT switch or something similar to switch between internal and external microphone and a MAX4466 opamp to amplify the audio. The small finger on the jacklug socket seems to connect directly to the switching line of the SPDT switch. Somehow it seems that U5 could be switching the power for the external microphone, but I can not see how what is actually switching U5, or maybe I just got confused switching back and forth between layers.
Thanks Alex for getting back. That's a shame that the 1.2.0 schematics haven't been released yet. I think that I would need these to ensure the work on an external microphone for bat recording is done properly and consistently between the versions. Is there a plan to release these at some point?
No, we haven't released the 1.2.0 schematics yet.
Many thanks Alex. Are the schematics for the 1.2.0 available anywhere? I have found a copy of the schematics for 1.1.0.
Hi Stuart, Yes, the analog circuitry is identical between 1.0.0 and 1.1.0. Both very different from 1.2.0 though. Alex
Does anyone know if the analog input circuitry is the same with the older 1.0.0 as the 1.1.0? I think that I am safe with testing that I am doing with external microphones with the 1.1.0 (the 1.1.0 schematics are available), but don't know about the 1.0.0.
I sent some of my elements to David in Belgium, he tested the microphone and compared to the internal (which is te same element) It seems to be working about just as well. I don't know if he has compared the recordings to something that uses an FG element. I wish I had the 1.2.0 version so I could do some test.
I just tried to mod my 1.1.0 so it might look more like te 1.2.0. I recorded a sweep from 150-20Khz which I played with a homebrew speaker, so we can only compare the two (maybe the mics work on higher frequency that te speaker). The SPU was used recording on middel gain setting, the FG on the highest setting.
Unfortunately connecting the FG did not work on my modded 1.1.0 board, so I attached V+ of the microphone to 3v3.
Connecting the Knowles SPU and FG seems possible by using the circuit I described earlier. The FG element however is very much less sensitive than the SPU so the FG might need like 20-30db more amplification. (I don't know any exact numbers) A recording will be a whole lot softer when you use an FG element. I have no idea of the gain setting in the audiomoth can compensate for that, maybe running on the higest gain setting will be good enough. The FG has a huge price compared to the SPU, I think the FG is around half the price of an audiomoth. It is also difficult to mount and you would probably double the price of the audiomoth. The knowles SPU element seems to be doing quite a good job on the ultrasound range.
I heard people that were not that enthusiastic about the Primo element. Unfortunately like the good old WM61, where you probably only find clones slold todat, you might also run into a fake Primo. If you want to try the SPU0410RL05-QB you could consider this model. ELV sells these with good documentation, adding just one resistor (about 5 kilo ohms) seems to work fine on my computer. I don't know the hardware of the 1.2.0. version board but what is described here in the link below, lets me think this will work. The attached picture shows a similar microphone to ELV Bausatz Mikrofon MEMS1. I will sent out one to a friend soon to test but maybe someone else has the chance to test this as well, specially a comparison beween the Knowles SPU and the Primo element would be nice. Micbooster also sells the SPU element but seems to need more external components.
AudioMoth should work well with the Primo microphones - https://micbooster.com/primo-microphone-capsules/97-primo-em258-mono-module-with-35mm-plug-10m.html
I don't have the audiomoth to test it, but a Knowles SPU0410LR5H-QB wired like this works fine on my PC soundcard. Maybe this is something you could try. I think the SPU0410LR5H-QB is the same element as on the PCB of your 1.2.0 version board. Kind regards, Edwin