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.

Help with simple voltage/current sensing relay.

Status
Not open for further replies.
Couldn't you use a single transistor to switch this?
 
I dont know


I was going to build one or both of the circuits shown on pg 1 of this thread.

I'm really clueless when it comes to this stuff
 
All you need to do is level shift right? You're not actually triggering the relay yourself that's the ECU that does it right? All you're trying to do is take that 4.6volts that the control panel puts out and covert it to 12 volts for the ECU?
Do you know how much current is being draw from that 12V connection to the ECU? Hopefully you have a multimeter you could find out.
 
Last edited:
Okay should be pretty simple. You said you tested the ECU unit by connecting 12V directly to it right? Assuming that it's easy. Set you multimeter to measure current, makes sure the probes are in the right plugs (the current measure plug is fused) and press one lead to the 12V line and the other probe to the proper ECU line, be careful not to touch the probe tip to the car chasis or any other ground or you'll blow the fuse on your meter in a hurry. Report back with what current it's drawing. Start on the highest setting your meter has (usually 10 amps) and if you don't get a reading or the reading is very low go to the lower setting if there is one.
 
And I just want to verify this, you said the ECU itself is what sends the signal to rev up the car and trips the relay that releases the clutch on the AC right? So ALL you're trying to do is adapt this 4.6 volt signal to the 12 volt the ECU requires, correct?
 
CORRECT!

The ecu will do everything so long as it gets that 12v signal which is all im trying to give it.

All i have available from the AC computer is a 4.6v signal with only 5.6 mA. So I was trying to find a way to use that signal to turn on a 12v signal.

But if there is a simpler way....
 
Have you tried connecting it directly to see if it works? If it's TTL logic all it needs is current, the 5ma might be enough, might not. With the 12 volt line shorted to the ECU (so the AC is on) what voltage do you get at that pin? Just use your meter in voltage mode, and attach the black wire to the car frame, see what voltage you get at the ECU pin while it's on.

Sorry I'm asking so many questions I'm not very familiar with the type's of inputs that are on car ECU units so I gotta cover my bases to try to understand what to recommend.
 
No, it doesn't work that way. That's the factory configuration. (Wish it worked!)

I'll check the voltage with that connected.... wont it just be vehicle voltage?

BRB
 
With the AC on there is full vehicle voltage at the ECU pin with 12v shorted... It's actually about 14v when the car is running
 
Hi.
I do not think you would be able to find a 5V - 1KΩ relay, but you could use an optoisolator to pass 12 V .
 
Opto isolate, thank you Externet! That would probably be easiest. Can anyone recommend a decent opto isolator for his requirements? The voltage and current are very low.
 
It's only been an hour! Chill!
 
Sorry I do not have the means to properly post a schematic with the message.

+4.6V-----------------|>|--------------------gnd (no resistor if current limited to ~5mA)
+13V-----------------C__E-------/\/\/\/------gnd (npn) /\/\/\/ = ~1KΩ ?

The emitter node E will go +12 when LED conducts
Nearly any optoisolator canibalized from an old telephone, fax machine or switching power supply etc. should work, instead of waiting for one to arrive on mail order.

Miguel
 
Last edited:
I'm not sure how to ID a optoisolator just by looking. Will this one work:

**broken link removed**

**broken link removed**



I do have an unused phone I opened up, but I only see transistors, resistors, diodes and capacitors... standard stuff. An optoisolator would have at least 4 pins no?
 
I'm not sure if the current transfer ratio is good enough on that one. It may work though.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top