“”I saw this signal injector kit so I built my modified version of it on a PCB. Notice that they used two PNP transistors and a positive ground, presumably to get pulses that were positive going. I used an astable multivibrator with negative ground like normal and I changed the output transistor to a PNP, 2N4403. This also gives positive going pulses. The pulse rep rate is about 2.8 kilohertz. The current drain on the 3V (two AA cells in series) is 0.24 milliamp. That’s low enough to use a CR2032 coin cell for the supply voltage. The small value output coupling capacitor makes the pulse very differentiated, in other words its width is narrow. I put a 0.1 microfarad capacitor in parallel with the 470 picofarad and it sounds a lot better using an earphone. The 470 picofarad by itself is barely audible and it’s just a hiss.
Update: I changed the output coupling capacitor from 470 pF to 3.9 nF.
I changed the .0047 uF to .01 uF.””
https://m.facebook.com/groups/ElectronicParts/permalink/3109674059221908/?ref=share&mibextid=NOb6eG
