Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Pleased with myself

Status
Not open for further replies.

throbscottle

Well-Known Member
I found how to add hysteresis to a photo-interrupter, now mechanical noise is banished!
So anyway, the interrupter's transistor outputs into the gate of a p-mos, originally to make the gear-tooth shaped waveform rectangular-ish I finally realised I can feed some signal back from the p-mos drain to the LED of the interrupter. Viola! An opto-schmitt trigger.
 
h.a.p.p.y. t.o. o.b.l.i.g.e.-
Screenshot_20210209_131405.jpg
I used the BSS84 in the original design because it's threshold voltage is similar to the nominal output from the photo-transistor, and the old circuit needed a p type transistor to drive it (also, it's simple) - so I just left it in. PL6 carries the 0v, LED and photo-transistor's collector for the interrupter. I need to change the LED feed resistor for a higher value now because on the high outputs it's in parallel with R48. C33 probably needs to be removed - it was part of my original noise suppression scheme (the other part of which was a 1uF to 0v on the collector pin which I also haven't actually taken out yet).

The input to the circuit is gear teeth passing through the photo-interrupter, so any vibration around the transition point created a lot of extra pulses. The next stage of the circuit is actually a noise discriminator (discussed elsewhere) followed by a monostable, but even these are fooled by the very worst of the vibration - so I needed to catch the signal at source. Without properly checking I seem to be getting a volt or so of hysteresis. Seeing noisy 1 and 0 states, but only in the area of about 500mV so that's ok.
 
I just realised the load is missing from the BSS84 - you'll have to visualise a 47k from drain to 0v. Otherwise it's merely funny...
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top