Hi!
Not directly arduino related, but hoping to get some advice on optocoupler selection.
I'm trying to replace the Q1 transistor im this curcuit, so that I can use a more flexible input signal.
Is there any optocouplers that are more flexible on the control current, that can handle big span in voltage with a single resistor value?
You need an opto coupler with one emitter and two receivers. You then use one of the receivers to output to your circuit and the other along with an op amp to control the brightness of your emitter along with your control signal.
Search for
linear opto coupler
For the circuit
Check out the HCNR200. It is a analog opto-coupler with high linearity.
Well the HCNR200 is just one type of the the opto Isolator I talked about in Reply #1.
Unless you have it on a board that has the extra circuitry, you still need to surround it with other circuitry. From the HCNR200 data sheet here is a typical circuit that uses that isolator.
Note that LED, PD1 and PD2 are the three parts of the HCNR200, all the other bits you have to build yourself. Also note in this schematic you need what is called a split supply with a +15V, Ground and -15V output.
Since I'm fairly novice with electronics, I think I don't want to over complicate things with adding so much circuitry. This is meant for the DIY'er, and I can use a small rotary selector or a jumper slot to select a suited resistor for each voltage range.
I appreciate the effort you put into guiding me, but I want to keep it as simple as I can.
By selecting the right resistors you might be able to get an opto to switch on any voltage from 5-24v.
Try 6k8 on the diode side and 33k on the transistor side
Might just do it - experiment ! The data sheet will tell you the max diode current and the transfer ratio ( current out / current in )
Put a 5.6v zener diode from Q1 base to ground, this will limit the voltage on Q1 emitter to about 5V whatever the input voltage (within reason). With 24V the current in the zener will be ~19v/10k or 1.9mA so you don't need a big zener. No need to mess around with opto isolators. A 5V input won't see the zener so circuit operation will be unaffected.
Yes less complicated at the expense of being not so linear and not so rail to rail.
I think the circuit should work from 5 to at least 55 V without any modification.
I'll just design it with a through hole resistor, so it is easily tweakable if needed.
Thanks for all your feedback.
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