Wow, a lot of activity here.
I was quite busy the last weeks so I did not have the time to check the forum.
The encodes I used are very cheap chinese encoders EC11 or sometting 10pcs only cost around USD 5.
It would probably help is we introduced some resistors into the data lines to the display but I am using quite a small housing so space is limited when I want to add extra resistors.
A BC847 is similar to the BC547, I used BC550 sinc it is a low noise version. I guess BC850 also is the low noise SMD equivalent. The A,B or C at the back determines the hFE, A is low C is highest.
I found the single transistor amplifier a good one. The transistor amplifier picked up less noise than the opamp I was experimenting with.
On high gain the audioboard becomes quite noisy, that is why I think it is important to have a small microphone amplifier.
I still want to try to get an opamp amlifier to work properly. I changed the board design so I can fit an opamp and hope I tried good enough to keep most of the noise out.
My reason to try this, is that the transistor output will be only around 1Vpp but the low noise opamp should be able to output around 3.1Vpp which is the maximum the audioboard can take as input.
Where stronger signals on the transistor amplifier start clipping and start to look like a square wave that might create harmonics the output of the opamp could still be a sine wave and have less harmonics.
I have also been thinking of a way to switch and bypass the amplifier but with the opamp that might not be necessary.
Anyway, I ordered for a bunch of PCB's that have all the modifications implemented so the 3v3 regulator is on the mainboard now and I can experiment with the opamp.
I ordered 20 pcs and like the other board I wille sell the ones I don't need via ebay or directly to people that want to build the bat detector.
I already had people asking if I was going to sell more boards, but these will be a little different for the first batch and they still have not arrived yet so be patient.
Oh I have been using the detector here near Koblenz, I heared a lot of noises, probably crickets or grasshoppers but I could not determine the sound.
It were fairly low frequency sounds maybe they sound better when frequency expansion was like 5 times in stead of 10 times. Unfortunately I forgot to place a memory card so I could not record.
Kind regards,
Edwin
I was quite busy the last weeks so I did not have the time to check the forum.
The encodes I used are very cheap chinese encoders EC11 or sometting 10pcs only cost around USD 5.
I know the splay is a great noise source. I was not able to get most noise out, I tried grounding some unused pins but it does not help a lot. What TFT pin do you mean that has 470nf/1uf on it?The TFT is also one of the major noise contributor : I add SMD capacitor ( 470nF , 1µF ) soldered on the TFT pin. Same think on bottom side 3.3V and GND under teensy and audio board
It would probably help is we introduced some resistors into the data lines to the display but I am using quite a small housing so space is limited when I want to add extra resistors.
A BC847 is similar to the BC547, I used BC550 sinc it is a low noise version. I guess BC850 also is the low noise SMD equivalent. The A,B or C at the back determines the hFE, A is low C is highest.
I found the single transistor amplifier a good one. The transistor amplifier picked up less noise than the opamp I was experimenting with.
On high gain the audioboard becomes quite noisy, that is why I think it is important to have a small microphone amplifier.
I still want to try to get an opamp amlifier to work properly. I changed the board design so I can fit an opamp and hope I tried good enough to keep most of the noise out.
My reason to try this, is that the transistor output will be only around 1Vpp but the low noise opamp should be able to output around 3.1Vpp which is the maximum the audioboard can take as input.
Where stronger signals on the transistor amplifier start clipping and start to look like a square wave that might create harmonics the output of the opamp could still be a sine wave and have less harmonics.
I have also been thinking of a way to switch and bypass the amplifier but with the opamp that might not be necessary.
Anyway, I ordered for a bunch of PCB's that have all the modifications implemented so the 3v3 regulator is on the mainboard now and I can experiment with the opamp.
I ordered 20 pcs and like the other board I wille sell the ones I don't need via ebay or directly to people that want to build the bat detector.
I already had people asking if I was going to sell more boards, but these will be a little different for the first batch and they still have not arrived yet so be patient.
Oh I have been using the detector here near Koblenz, I heared a lot of noises, probably crickets or grasshoppers but I could not determine the sound.
It were fairly low frequency sounds maybe they sound better when frequency expansion was like 5 times in stead of 10 times. Unfortunately I forgot to place a memory card so I could not record.
Kind regards,
Edwin