Hall Effect/Inductance ammeter spark plug wrap help

ronv

Joined Nov 12, 2008
3,770
It is quite likely that the little spike won't turn on the opto. The circuit I posted protects the circuits with the cap in series and the zener diode and the regular diode.
 

Thread Starter

JBernard

Joined Aug 8, 2013
46
do you think i could implement the part of the circuit you drew up before the transistor, would that smooth the pulse out like it did before. then just use the opto instead of the transistor?
will the zeners be able to handle that high of voltage?
 

Thread Starter

JBernard

Joined Aug 8, 2013
46
hey ronv,
that scope picture i posted was off a similar application, i *think* mine will give a similar waveform, but at a different voltage. i know for sure my system is 0-40V range, but have another friend that i'd like to swap the meter to and his is 0-100V, so i'd like to have some headroom, maybe 150V+ to be on the safe side.

with the optocoupler its required for the negative side of the emitter to be connected to ground to work? would this cause an issue with my application because it will be wired off an accessory or killswitch lead, thus always shorting out? in the sketch i drew up you can see how i routed the opto in-line on the hot side, but maybe this wont work?
thanks!
 

ronv

Joined Nov 12, 2008
3,770
Yes, the way you drew it will work, but keep in mind the output will be inverted from the first circuit so you will need to change your code.
Make the input cap 5 or 600 volts just to be safe.
 

Thread Starter

JBernard

Joined Aug 8, 2013
46
ron,
thanks for the reply. pardon my ignorance... but with the opto, wiring both pads 1 and 2 to the voltage+ line, wouldnt that be like hooking both the anode and cathode of an led to the positive voltage. how does the led work without cathode to ground?
 

Thread Starter

JBernard

Joined Aug 8, 2013
46
thanks for taking the time to draw that out in the sim. i think i'm having a better understanding now, will do a layout mockup in a bit and see if i have it in my head correctly.
do i need high voltage caps on C1 and C2 or just C1?
 

Thread Starter

JBernard

Joined Aug 8, 2013
46
ah, i see what youre doing now. makes sense. i will get a couple parts i dont have coming and hopefully have a prototype up running soon!
one other question i did have....
ive been powering the arduino with a 9V but will be using a smaller microcontroller in the future. something like an ARM Cortex M0 that i can run on a micro sized 3.7V lipo, maybe a low mAh package like 150-500.

saying that, and speaking from electronics ignorance again. the way its set up now, reading +5V as off, then reading 0V as on, is that actually consuming any current when its on and off? when its on its dumping the 5V rail to ground right?
if this design is using battery life, what other ideas could be done to make it as small draw as physically possible?

thanks again!
taylor
 

ronv

Joined Nov 12, 2008
3,770
We could get rid of the opto and make R3 just small enough to make sure the mico can read it. Then it only draws current when it is on.
 

Thread Starter

JBernard

Joined Aug 8, 2013
46
ron,
got the board hooked up on a protoype pcb and after a bit of troubleshooting and having some diodes backwards and the like, i think i have it hooked up correctly but its still giving me some issues.
its showing the out voltage is the same as when the front end is powered with 20V or not. so it appears the opto isnt being triggered?
please let me know if you can think of anything that i could be doing wrong....

i see that base (pin6 on the opto isnt hooked up to anything?

also, is this an inverse sensor like the others (shows 5V when off/nothing detected on front end, and near 0V when on)? if so, isnt the 1k resistor knocking it down below 5V?

edit- C1 im using is 500V .01uf ceramic

 
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ronv

Joined Nov 12, 2008
3,770
It needs pulses to work because C1 blocks the dc voltage. You could move the 20 volts to the other side of C1 just to test it.
 

Thread Starter

JBernard

Joined Aug 8, 2013
46
nice thinking, that solved that issue!
reading .484V when off, and when powered via 20V input reads 5V.
thank you, you rock!
 
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