Hi All
I need to build a 3.3v arduino clone based circuit powered by a motorcycle (12v). It also needs to detect turn and stop signals. Due to the fluctuation in voltages, I figured some kind of opto-isolation would be a good idea.
My circuit is attached and here: https://www.circuitlab.com/circuit/gt47md/tx4/
The opto isolator will be 4ch. I will be using 3 channels
Would someone mind critiquing it?
Thank
Mark
What help do you need?
Want to make sure the components are correct values and if anyone thinks it won't work. And if I'm sourcing or sinking too much current. One thing I'm not sure about is the 1K resistor at top. If I have three opto isolators, I need enough current to drive 1 or all 3. I assume I'd connect the other two in parallel (i.e. each with own 1K resistor)
Haven't bought the opto isolator yet, so can't bench test anything
The pinout looks wrong. There are 16 pins. You use pin 1 and 2 for a diode correctly.
http://www.cel.com/pdf/datasheets/ps2501.pdf
pins 3 and 4 are wrong .
Try again, using the correct pins numbers.
Sorry used pin-outs from PS2501-1, outputs should be 3 and 4 should be 15 and 16 respectively
I've inserted the full chip now
The 7805 requires decoupling capacitors on input and output. Also the 7805 is not rated for automotive use - you may need better
protection against the spikes and noise on the 12V power - a filter to cleanup the 12V line might be a wise precaution.
Diode on opto-isolator is 1.4v forward voltage at 10mA. A 1.5K resistor on 12v (10-15v) side may be better.
Thanks for replies guys. Can anyone recommend a voltage regulator for automotive use (ideally 3.3v out, but could work with 5v)
Would this be suitable for automotive? Look like it would to my naïve eye:
Just found out they are $30+ each, so will skip that
The problem with vehicle power systems is that sometimes there can be big noise spikes (starter
motors, ignition break-through), so you either have to be lucky (have a well-behaved vehicle
that doesn't generate anything too bad), or add a power filtering circuit. Some combination or
RF chokes and electrolytics, possible a zener clamp too...
Possibly the simplest arrangement would be fuse, RFC and TVS clamp (TVS diodes are basically
high power zener clamps), then the regulator circuit.
Another approach is to find a good DC-DC converter module with a wide input voltage range (something like
8V - 48V ?) and use that - such switch-mode regulators will handle brown-outs and most over-voltage spikes
without difficulty, and furthermore be more efficient than a linear regulator.
They are usually fully isolated between input and output too, which might be a good thing.
Thanks for reply.
I came across this, which looks like it might do the trick (unless I missed something): http://www.fairchildsemi.com/ds/KA/KA278R05C.pdf
I only need less than 100mA, so it's somewhat overrated, but cheap as chips 
Regards
mark
Also came across this.
Seems ideal
Designed for vehicular applications
$1.65 each
I've updated my design and added the second input (will be 3 total)
I'm not sure if I need to replicate the diodes (DL and DR) and Caps (CL and CR) on each input
Also not sure if I've got R1 and R2 wiring correct
Would someone mind verifying?
TIA
Mark
mark_anderson_us:
I've updated my design and added the second input (will be 3 total)I'm not sure if I need to replicate the diodes (DL and DR) and Caps (CL and CR) on each input
Also not sure if I've got R1 and R2 wiring correct
Would someone mind verifying?
TIA
Mark
It looks like you have A4 & A5 set HIGH with pull-up resistors. Then, when opto-coupler is triggered/activated, it will turn on and pull the signal LOW. Is that correct?
IF you wanted the opposite (Arduino inputs pulled LOW, and triggered to HIGH from turn signals) something like this would work -
Either way should be fine. Just depending on what you want/expect & code for. (Sorry, I can't remember if I should already know that from previous posts.... 
)
Thanks for pointing that out Dave.
As luck would have it (that's all it was), that's what I actually wanted (my test version using 5v inputs is designed like that)
Hi Guys
I built my circuit (final version attached).
I used a BEC in the end; however, I can't get my arduino inputs to trigger. I need (pin 16) to go low when 12v is applied pin 1 of the 2501-4
I've annotated the circuit with measurements I took when 12v was applied to pin 1
Anyone got any idea what I'm missing
Regards
Mark
