# "Dangerous Arduino Voltage" ahahaha.

Came across a venus fly trap project using an Arduino.

Ah… now on step 9. (Refer to attached image)

Maybe someone can enlighten me regarding the dangerous arduino voltages and the need for an optocoupler

It's from the internet, it has to be correct. ;)

Voltage isn't dangerous, current is.

You can scrape half that circuit as its not needed in this application, all the voltage and current going to the plant is being driven by the op-amp.

Its a little hard to explain without redrawing the circuit, but basically you can ditch the TLC621 chip, connect D2 to the + pin on the op-amp as the voltage on the output is determined by the Vcc input. The other side of the pumper can just go to ground.

I might have missed something but don't have time to explain right now.

I see no reason for the opto coupler either.

My first thought was, that maybe 5V would damage the plant. But the tutorial uses a 3V battery pack, and that does noes leave much difference.

I'd just use a voltage divider and the signal from the arduino.

My best guess is, that the text has been adapted from somewhere else, and the setup just carried over without much thought?

cjdelphi: Maybe someone can enlighten me regarding the dangerous arduino voltages and the need for an optocoupler :D

It's all about grounding.

You can sit safely on a 400kV powerline so long as you call it "ground".

But ... don't reach down and touch an Arduino.

If you do not like the opto in the circuit, then you have to get a 5 V tollerant Venus Fly Trap plant (very rare, very expensive, better to use the opto for level conversion....)

The “opto in the circuit” doesn’t control the voltage whatsoever.

The Vcc to the op-amp does. The op-amp is connected as a feed back comparitor, meaning as long as any voltage above 0V is applied to the + pin, the output will be driven high which as we can see is 3V.

I took 10 sec to modify that circuit in paint for what is the equivalent effect with fewer parts, I even added a LED indicator just for kicks so you know its on, using the un-used op-amp.

I didn’t add it in but 40mA seems a bit high (the sourcing current of the op-amp) for a plant, if you wanted to be safe with your plant I’d add a resistor in series to the plant of 1K ohm and then lower it as required if you get no movement.

Edit: There is one thing wrong with my hasty circuit, you must use a voltage divider to bring the 5V D2 pin to a voltage range of 1-2V before connecting to the + pin on the op-amp.

The optocoupler isolates the Venus flytrap from the “dangerous” voltages of the Arduino and connects it instead to the “safe” voltages from the batteries. Inside the optocoupler is a little LED and a photodetector.

dangerous and safe are in quotes, I think a punn was intended. I'd put them IN CAPITALS if I was serious.

Tom..... :)

Actually, I've noticed that many people are using quotes as emphasis. First in emails and texts, now everywhere. I hate it.

polymorph: Actually, I've noticed that many people are using quotes as emphasis. First in emails and texts, now everywhere. I hate it.

Why? What do you prefer, CAPS, bold, italicized, different font size, different color?. How do you "emphasize".

I don't use quotes. Quotes mean that you are, well, quoting someone. Or that you mean it ironically, which may be the case here.

It should -not- be used for emphasis just because someone is using plain text and cannot change fonts or font properties. I prefer to use dashes or caps, in those cases.

Not a pun, either. Or did I miss something?

retrolefty:
What do you prefer, CAPS, bold, italicized, different font size, different color?. How do you “emphasize”.

For emphasis, either bold or underline.
If those aren’t available, then it’s CAPS.

[Going OT, so sorry.]

polymorph: I don't use quotes. Quotes mean that you are, well, quoting someone. Or that you mean it ironically, which may be the case here.

It should -not- be used for emphasis just because someone is using plain text and cannot change fonts or font properties. I prefer to use dashes or caps, in those cases.

When using plain text, the convention for emphasis is either word (indicating underline) or word (indicating bold). Caps is 'shouting' and should be avoided. DON'T YOU AGREE? :grin:

I agree -=completely=-.