Putting voltage into an output...break it?

[212]

OK...I know you put a diode across a relay to keep it from breaking the Picaxe chip when it turns off.

Now...I'm working on RF camera with video controller, and I need to share the audio channel on the RF transmitter. I intend to have the cameras audio and the tone, used to control my VCR controller, going through the same pipe....so to speak. I'll send a tone with Picaxe, but the camera's audio will be there too. That should be OK I suspect, but the tone will only be needed a few seconds, then....well...then the cameras audio will be putting audio into the Picaxe output pin. Can't use a diode here, so is this a problem?

I'd use a DPDT relay to separate them if I had more output pins...might need another chip huh??? orrrrrrr...can I get away with it???

 

[leftyretro]

OK...I know you put a diode across a relay to keep it from breaking the Picaxe chip when it turns off.

Now...I'm working on RF camera with video controller, and I need to share the audio channel on the RF transmitter. I intend to have the cameras audio and the tone, used to control my VCR controller, going through the same pipe....so to speak. I'll send a tone with Picaxe, but the camera's audio will be there too. That should be OK I suspect, but the tone will only be needed a few seconds, then....well...then the cameras audio will be putting audio into the Picaxe output pin. Can't use a diode here, so is this a problem?

I'd use a DPDT relay to separate them if I had more output pins...might need another chip huh??? orrrrrrr...can I get away with it???

Just use a capacitor (0.5mfd should work ok) between the picaxe audio output and the transmitters audio input. I'm pretty sure that would protect the picaxe output pin pretty much.

Lefty

 

[westaust55]

Tones from the PICAXE are only a square wave switching between Vss (0V) and Vdd (~5Vdc).

Some audio signals are at a line level of only 1 Vpeak (from memory) but if the audio ac signal could be higher than Vdd (4.5V or 5V) a capacitor alone will not block the higher voltage ac – capacitor blocks DC but not AC component.

So check the audio voltage levels and if greater than Vdd then a diode (with the anode to the PICAXE) as proposed would still be good insurance against PICAXE damage.

 

[212]

"Sounds"... like I may be in business then, thanks! The audio from the camera will be around 1 Vpeak, so the Picaxe should be OK, and I will still try using a diode there anyway. The cap Lefty said to use might keep the Picaxe from hurting the camera audio output too, I thought all sounds were ac??

I wish all I had to do was play with these projects, but I gotta go make some $$$ to buy a gallon of gas too...maybe $$$$$ by the time I get there.

 

[hippy]

A lot depends upon exactly what it is you're connecting together. Simple diodes block current flow in one direction, resistors can limit current flow, capacitors block DC, but you may need op-amps or logic gates to do mixing of some signals.

"I thought all sounds were ac??

Depends on what you consider as your reference voltage - a +/-250V "AC" signal can also be +500V/0V or 0V/-500V "DC". A PICAXE output is notionally 0V/+5V but can also be considered as 0V/-5V or even -2.5V/+2.5V.

Don't forget it's 'Alternating Current' not 'Alternating Voltage'; does current flow into or out of your reference point.

 

[212]

You had to go ask and intelligent question like that didn't you lol... I have to admit I have no idea what I have here. Tell ya what I can do though, I'll use the filter I found in the tone wizard help file, and add a volume control VR to it like I have done before. Then I'll use a couple of 10K resistors on each audio output for a mixer like I found. I'll put in a diode too, on the Picaxe output pin, and I'll even use the cap like suggested. If this works then I'll be thrilled and will post a drawing, and if not, then I'll beg for help again

 

[Dippy]

And don't forget the effect capacitors will have when bunging a square wave through them.
(It's prob not significant but I thought I'd just remind you. Have a look on a scope. Its just something to remember with reactive components.)

You could just use resistors into a simple op-amp mixer circuit. I think that would require an op-amp and 3 or 4 resistors.

From the PICAXE perspective , when not parping, you could just make the O/p into a high impedance input. But not knowing the other device at all then that is only half the story.