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wespo / analogShield

Analog Shield Library
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write negative voltage #10

Open machinehistories opened 6 years ago

machinehistories commented 6 years ago

Is there a way to write out a variable negative voltage using the dac. Can one of the negative voltages on the power supply be used as a reference and would this enable one to write out a negative voltage. thanks

thejbw commented 6 years ago

If I understand the question...The DAC can write out voltages -5V to +5V it takes unsigned 16-bit integers (0 to 65535), so analogWrite(0,0) would write -5V to channel 0. Writing 65535 would put out 5V, and writing halfway between (32768) would write out 0V.

machinehistories commented 6 years ago

That's so great I will try it tonight. I know it worked that way with the analog read but I wasn't sure if the write could produce + and - voltages. We are trying to use the board as a potentiostat to do some electrochemistry experiments and I think it might just work so long as I can write out variable + and - voltages . I thought I tried it and I only saw a positive reading on the voltmeter but I probably did something wrong.Do I simply run the wire from the channel pin to external device and from external device to ground or do I need to use the power supply rails to use the + and - voltage outputs. thanks for you answer and for your hard work in making the library - jason

On Tue, Jul 17, 2018 at 10:42 PM thejbw notifications@github.com wrote:

If I understand the question...The DAC can write out voltages -5V to +5V it takes unsigned 16-bit integers (0 to 65535), so analogWrite(0,0) would write -5V to channel 0. Writing 65535 would put out 5V, and writing halfway between (32768) would write out 0V.

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/wespo/analogShield/issues/10#issuecomment-405815515, or mute the thread https://github.com/notifications/unsubscribe-auth/AZlqVC4RPQ2deucqWjFpKB-uZrwywUaNks5uHsq-gaJpZM4VT-Zl .

wespo commented 6 years ago

You should only need the external device and ground. That said, you also need to know the current draw of the device. The analog shield DAC (analog output) is buffered by an op-amp and can put out a tens to low hundreds of milliamps, but if your application requires higher current, you will likely need some sort of buffer amplifier.

The output of the dac can definitely go negative with respect to the analog shield ground. Please note that none of the outputs are isolated, so it's a negative voltage referenced to the arduino ground.

machinehistories commented 6 years ago

I tried it out and I still had issues but I changed boards and now it is working as expected thanks again

On Wed, Jul 18, 2018 at 4:06 PM wespo notifications@github.com wrote:

You should only need the external device and ground. That said, you also need to know the current draw of the device. The analog shield DAC (analog output) is buffered by an op-amp and can put out a tens to low hundreds of milliamps, but if your application requires higher current, you will likely need some sort of buffer amplifier.

The output of the dac can definitely go negative with respect to the analog shield ground. Please note that none of the outputs are isolated, so it's a negative voltage referenced to the arduino ground.

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/wespo/analogShield/issues/10#issuecomment-406101373, or mute the thread https://github.com/notifications/unsubscribe-auth/AZlqVJxJDs4ZzMAl2BgNhLE2hplHl4Bhks5uH799gaJpZM4VT-Zl .