Jellybean voltage detector circuit - Page 1
Forum section: electronics / projects

author: kaz911
author_rank: Super Contributor
timestamp: July 13, 2016, 07:35:24 am
content: Hi,I'm a bit stuckI have a circuit with multiple voltage inputs that needs to activate an opto-coupler with minimum 7-14 mA.I have it working with zener diodes - and have tried with small voltage regulators as well. But I want it to be a bit more flexible so input power can be from 9v to 36v - and components HAVE to be easy to find - as I plan it as a "DIY" / Open Hardware board. All inputs are "OR"'ed together with diodes so any 1 of 4 inputs can turn on Optocoupler which then turns on a relay.So what would be the CHEAPEST way to implement a voltage detector with LEAST amount of components. Maybe some high voltage low amp voltage regulators are the best choice for ease of assembly.But does anyone have better ideas? Any obvious ideas I have overlooked?

author: Rerouter
author_rank: Super Contributor
timestamp: July 13, 2016, 07:40:27 am
content: Optocoupler and a constant current diode, then have a 4 diodes OR into that?

author: kaz911
author_rank: Super Contributor
timestamp: July 13, 2016, 07:43:31 am
content: yes I'm OR'ing them now with diodes.

author: Rerouter
author_rank: Super Contributor
timestamp: July 13, 2016, 07:45:13 am
content: Thing is the constant current diode would mean no need for any resistors on the optocoupler,

author: kaz911
author_rank: Super Contributor
timestamp: July 13, 2016, 07:55:12 am
content: yes - but I have quite spread out temperatures - So i'll have to do some calculations. Temperatures can be from probably -30c to +80c in the extremes and CC diodes needs extra compensation for temperature drift as far as I remember.So over to DaveCad and do some calc's

author: Kalvin
author_rank: Super Contributor
timestamp: July 13, 2016, 08:12:33 am
content: Four "OR"-connected 1N4001 diodes driving the opto coupler and the constant current sink made from jellybean BJTs and resistor.Edit: Maybe an additional zener in series with the current sink if you need a bit sharper and more precise detection.

author: Kalvin
author_rank: Super Contributor
timestamp: July 13, 2016, 09:15:05 am
content: Four 1N4001s connected as "OR" feeding a jellybean LM317 set for 7V output voltage which drives the opto coupler and the 700ohm current limiting resistor. At 10mA and 36V input voltage and 7V output voltage the LM317 has to dissipate approximately 0.3W which is not too bad.

author: Kalvin
author_rank: Super Contributor
timestamp: July 13, 2016, 09:22:46 am
content: Just drop the opto coupler, make the "OR" using 1N4001s and drive a small 9V relay directly with the constant current sink/source made from the jellybean BJTs?

author: Zero999
author_rank: Super Contributor
timestamp: July 13, 2016, 09:45:45 am
content: The LM317L configured for constant current.

author: kaz911
author_rank: Super Contributor
timestamp: July 13, 2016, 04:59:15 pm
content: the part that is turned on - must be power isolated from rest. It's for marine use - where you have a CAN bus with 12v (5 wires - 2 data + 12v/gnd + shield) supply running on it. The 12v must be isolated - so no choice there.But rest of boat can run 12v or 24v - but some big diesels push up to 32v out on the alternators. And some badly maintained boats only manage 11-12v.so have to be ready for anything. But practical if it shuts down around 9-10v not to have that drain the batteries too. But DaveCad next weekand I'll update later.NMEA 2000 is great - but they forgot some features like "selective ON/OFF" - so if you have NMEA powered displays - every time you turn NMEA bus on - everything lights up. So my little board is an isolator - so you can say when Chart-plotter gets 12-24v - then turn on the NMEA powered displays as well. But if you turn Chart-Plotter off - turn off the other displays if you want. But leave GPS/Weather station running on the NMEA network. Or it could be engine instruments - if they are on - you might want NMEA display on as well. So bus powered devices are great for many things. But it is also great to be able to turn them off...So idea is that any signal from 12 or 24 volt systems should be able to turn on / off part of the NMEA network.And since there are plenty of expensive things for Boats - I just want to put it out there for people to make themselves for not a lot of cost - and easy component sourcing.