Maker Pro
Maker Pro

Tri-level composite signal from microcontroller

epicedium

Jun 29, 2017
3
Joined
Jun 29, 2017
Messages
3
What is the easiest way to generate this pulse from a microcontroller running at 3v3? I have IO pins and PWMs available.

https://en.wikipedia.org/wiki/Tri-level_sync

I haven't dealt with negative voltages before, and I'm not that familiar with analogue electronics (other than simple opamp circuits). My first instinct is to generate -3v3 (somehow?) then use 2 or 3 microcontroller pins to switch 2/3 mosfets or transistors with resistors dividing voltage, but I do wonder if there's a better/ simpler way.

It doesn't seem possible/appropriate to create a virtual ground unfortunately, as the composite signals go out over BNC using chassis ground.
 

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
The wikipedia article says there is no DC, perhaps a capacitor in the line would be sufficient.
There are integrated circuits which can give a low current negative supply, I have never used one.
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
The opamp would need a dual-polarity supply if you want it to put out a negative-going pulse.
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
Duke suggested a cap. Here's a sim. Good enough for your needs?
3-level.PNG
 

epicedium

Jun 29, 2017
3
Joined
Jun 29, 2017
Messages
3
Alec_t, Duke- the cap, it may well be acceptable, yes! I'll simulate it into a 75Ohm load and experiment- my experience with AC is pretty minimal so I don't really grasp how it works. I assume that I could clamp the spike with diodes and that the magnitude and duration of the spike are a product of the capacitance and load. I'll report back once I've had a play around. Thanks!
 
Top