This is a HID based USB device that capture DTMF Caller IDs from land line and send it to CIDL-Manager software over USB. There is no driver needed for device cause it works as HID device and it should be recognized and works in most Operating Systems.
The schematic may be incorrect, as the LM358 has no feedback resistor. What is the intended gain and frequency response of the input circuit?
Please check.
It would be polite to acknowledge authorship of the source code on the Github page, for example
11.09.2019 V0_08P Author 6V6GT DTMF decoder library - #75 by 6v6gt - Audio - Arduino Forum
I think he is ok with it and referenced it. You could see our conversation here:
The Lm358 configured in very high gain and filter mode. I'm not a op-amp expert but this project made by experimenting and it is working for 5 months without problem.
Very strange! The op amp is configured as an integrator, with no DC feedback.
I have no real scope to prove it but what I saw using ZaidaScope was not a saw tooth waveform. I guess it act as a low pass filter with very high gain. Actually at first I did add the DC feedback but it increased decoding error.
Actually, the signal amplitude is reduced (see above). Here is the simulation of the circuit in post #18, using LTSpice. If It works, fine, have fun!
It don't know much about this simulation but the circuit surely amplify a 100mvpp to 1.5vpp and it does like a positive gain. Please share the simulation file.
Which circuit? The one on the Github repo won't work as a linear amplifier, and it is not the same as the one I simulated (below, from your cross post, reply #18).
lm358_amp_AC2.asc
Version 4
SHEET 1 1436 680
WIRE 432 16 64 16
WIRE 560 16 432 16
WIRE 432 80 432 16
WIRE 752 80 624 80
WIRE -48 96 -160 96
WIRE 64 96 32 96
WIRE 112 96 64 96
WIRE 224 96 112 96
WIRE 320 96 288 96
WIRE -160 112 -160 96
WIRE 752 128 752 80
WIRE 112 144 112 96
WIRE 144 144 112 144
WIRE 320 160 320 96
WIRE 320 160 208 160
WIRE 432 160 384 160
WIRE 480 160 432 160
WIRE 144 176 112 176
WIRE 560 176 560 16
WIRE 624 176 560 176
WIRE 64 192 -160 192
WIRE 112 192 112 176
WIRE 112 192 64 192
WIRE 64 288 64 192
FLAG 64 288 0
FLAG 176 128 VP
FLAG 176 192 VM
FLAG 752 224 0
FLAG 832 224 0
FLAG 752 144 VP
FLAG 832 144 VM
FLAG 624 224 0
FLAG 432 240 0
FLAG 480 160 OUT
SYMBOL cap 224 112 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C1
SYMATTR Value 10nF
SYMBOL voltage 752 128 R0
WINDOW 0 -55 17 Left 2
WINDOW 3 -59 94 Left 2
SYMATTR InstName V1
SYMATTR Value 5V
SYMBOL voltage 832 240 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
SYMATTR InstName V2
SYMATTR Value 0V
SYMBOL Opamps\\opamp2 176 96 R0
WINDOW 3 20 122 Left 2
SYMATTR Value lmx58_lm2904
SYMATTR InstName U1
SYMBOL res 48 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 1K
SYMBOL res 80 112 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 12K
SYMBOL voltage -160 96 R0
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR Value2 AC 1
SYMATTR InstName V3
SYMATTR Value ""
SYMBOL res 416 64 R0
SYMATTR InstName R2
SYMATTR Value 100K
SYMBOL res 416 144 R0
SYMATTR InstName R4
SYMATTR Value 100K
SYMBOL cap 384 144 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 100nF
SYMBOL cap 608 160 R0
SYMATTR InstName C3
SYMATTR Value 100µF
SYMBOL res 608 64 R0
SYMATTR InstName R5
SYMATTR Value 1K
TEXT 200 256 Left 2 !.inc lmx58_lm2904.lib
TEXT -216 392 Left 2 ;to add ti lmx58_lm2904 model: move .lib file to docs/ltspice/lib/sub, add opamp2 to \ndrawing, change value to "lmx58_lm2904", add .inc lmx58_lm2904.lib. \nneed symbol? edit opamp2.asy (change name), save as lmx58_lm2904.asy
TEXT -304 -40 Left 2 ;https://forum.allaboutcircuits.com/threads/problem-with-tl431-in-ltspicexvii-unknown-subcircuit-called-in-xu1-n001-n004-tl431-tl431-ed.160848/
TEXT -184 272 Left 2 !.ac dec 10 10 4000
Here is a typical op amp audio amplifier circuit. This one has voltage gain 82. For a gain of 10, reduce R5 to 100K. Add a suitable capacitor in parallel to R5 to reduce the high frequency response (low pass filter).