Electrical question.

[frankzappa]

Is it OK to plug the 3.3V to the ground pin with only about 250 ohms of resistance. Is that bad for some reason?

Thanks.

 

[mlu]

3.3V/250 ohm = 13.2 mA, its like a couple of leds, so should not hurt, but why waste power.

 

[frankzappa]

3.3V/250 ohm = 13.2 mA, its like a couple of leds, so should not hurt, but why waste power.

I'm not connected to a battery so not worried about that.

I'm using two resistors to create a voltage divider as a midpoint voltage reference for some piezos. I can use higher value resistors but they will ripple much more.

The reason why I'm asking is because I have a PCB with that circuit and for some reason the teensy won't power up when it's connected to the circuit. It powers up fine when I unconnect it. I'm thinking maybe I short circuited something that makes the teensy not power up. I had a hard time soldering the PCB and must have fried something on it.

 

[MarkT]

Surely they won't ripple any more. The voltage at the mid-point of the divider will have the same amount of ripple with 10k:10k as with 120:120.
It will have a higher source impedance, is that the issue? That can be fixed with some bulk decoupling between the midpoint and ground - as often
seen with a virtual ground.

 

[frankzappa]

Surely they won't ripple any more. The voltage at the mid-point of the divider will have the same amount of ripple with 10k:10k as with 120:120.
It will have a higher source impedance, is that the issue? That can be fixed with some bulk decoupling between the midpoint and ground - as often
seen with a virtual ground.

Aha, well I have no clue about what it is. All I see is low frequency periodic waves. That’s what I meant by ripple. I just made a circuit that works and just tried different things. I noticed that the lower valued resistors produced a much cleaner signal. I tried adding some small capacitors here and there but it made no difference. After digital filtering the signal is cleaner with no capacitors. I think the high frequency noise helps with cleaning up the signal when you filter it.

What value capacitor would I need to get rid of the low frequency oscillating noise if I decide to use higher value resistors.

Also what is the benefit of using higher value resistors?

I have three op amps connected to the same 3.3V pin. Maybe it would not be enough current if the virtual ground draws too much. Circuit seems to work great. Only thing is that the board died on me but I think I may have fried something when I soldered it.