What is the function of this circuit?

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geb
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What is the function of this circuit?

Post by geb » Tue Jun 17, 2008 10:32 am

Image


A three relay board with three (same value) resistors and eight input posts.

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Sambuchi
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Post by Sambuchi » Tue Jun 17, 2008 11:43 am

I have a good idea but WOW..

There needs to be some node dots on this guy.

Where did you get this schematic?

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haklesup
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Post by haklesup » Tue Jun 17, 2008 1:42 pm

Pin 7 is common to the three SPST switches. Pins 5,6,8 are the other side of those SPST switches.

Pin 1 is ground or common for the relays (it could be vdd in a negative logic configuration). Pins 2, 3, 4 are the signal lines that close the relays. In parallel to each relay is a resistor. the purpose is unknown because I do not know the nature of the signal for pins 2,3,4 but it likly divides the voltage to make compatible the signal voltage and the relay coil voltage. It could also be to damp Back-EMF as an alternative to a diode snubber.

The polarity, voltage, current and waveform of the signals applied to the relays is unknown. It could change the interpretation a bit.

geb
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Post by geb » Tue Jun 17, 2008 3:58 pm

You might have guessed by my other post that I'm hoping I might use this as a flip flop circuit. It's a three relay board out of a Honda Civic. Nippon Denso. 12vdc. Underdash... probably for doorlocks or blower relay or something like that. The resistors intrigued me as well as the rationelle for putting all of this on one little board. I was hoping there might be a way to wire the 8 inputs (that was immediately obvious to someone other than me) to
enable it to flip flop the output of one of the relays.

I drew the circuit myself using a program called Dia. I left out any node markings hoping it would be self explanatory. There are no junctions where any of the lines cross over one another.

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Bob Scott
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Re: What is the function of this circuit?

Post by Bob Scott » Tue Jun 17, 2008 9:58 pm

geb wrote:Image


A three relay board with three (same value) resistors and eight input posts.
Each of the 3 "resistors" are directly wired in parallel across each of the coil windings, probably to absorb flyback pulse when de-energised. Could they be capacitors instead? Resistors OK but not the ideal component for this job.

Other than that, the circuit simply 3 independent relays except for a common reference at the input and another common reference at the output. My guess is blower motor. Of course, it could also me multiple use also. Three relays in my car are fuel pump + horn + AC clutch.

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Post by Engineer1138 » Wed Jun 18, 2008 8:19 am

How much real estate is available for the DPDT switch and what is the current capacity? Maybe if I have time I can just make one and send it out. You've got my interest piqued now :-)

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haklesup
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Post by haklesup » Wed Jun 18, 2008 10:05 am

A flip flop, not by itself at least not a D FF, maybe an RS FF. For example with NMOS technology it takes 2 transistors to make a NAND gate and you need 2 NAND gates to make a latch and even more to add the FF functions of clock, reset or clear. I compare to NMOS because you can emulate with a resistor as a pullup and the relay as the switch to ground.

I suspect the resistors are actually diodes as that would make the most sense. Why use a divider resistor when you can just get the right relay coil resistance in the first place. relays are also insensitive to noise so a cap would be unnessary.

Couple that with some 12V CMOS logic and you can have a FF. Add

You could generally make a latching relay from a DPDT. By wiring two in parallel you can emulate a DPST n.o. switch. The load side is not as flexible as with a DPDT (cannot have n.c. contacts) but it can still latch.

Use a momentary switch from 12V in series with two relay coils which will close the two n.o. contacts. on one pole, you connect the common to 12V and the n.o. contact to the relay coils. When you press the button, both relays close and one of them sustains power to the relays. The other n.o. pole of your composite switch can be connected to the load.

The third relay if it were n.c contact could be used to reset the latch instead you will have to add another momentary n.c. switch to do that. You could use the third switch to invert the output. you would need to pullup the third coil using a resistor and then short that node to ground using the output of coil 2 (pole 2). This would waste power and get hot though depending on required coil current.

Do you follow or do you need a schematic?

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Post by Engineer1138 » Wed Jun 18, 2008 4:58 pm

I forgot to ask if your requirement that the previous state be remembered without power is no longer applicable? Because while you can make latching relays from other relays, they need power to hold the state.

As long as you're looking at relays from cars, there was a cam-latching (pulse on/pulse off) relay used in older Volvos. The same mechanism is used in other latching relays, but I think you already said they were too big.

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MrAl
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Post by MrAl » Thu Jun 19, 2008 12:17 pm

haklesup wrote:A flip flop, not by itself at least not a D FF, maybe an RS FF. For example with NMOS technology it takes 2 transistors to make a NAND gate and you need 2 NAND gates to make a latch and even more to add the FF functions of clock, reset or clear. I compare to NMOS because you can emulate with a resistor as a pullup and the relay as the switch to ground.

I suspect the resistors are actually diodes as that would make the most sense. Why use a divider resistor when you can just get the right relay coil resistance in the first place. relays are also insensitive to noise so a cap would be unnessary.

Couple that with some 12V CMOS logic and you can have a FF. Add

You could generally make a latching relay from a DPDT. By wiring two in parallel you can emulate a DPST n.o. switch. The load side is not as flexible as with a DPDT (cannot have n.c. contacts) but it can still latch.

Use a momentary switch from 12V in series with two relay coils which will close the two n.o. contacts. on one pole, you connect the common to 12V and the n.o. contact to the relay coils. When you press the button, both relays close and one of them sustains power to the relays. The other n.o. pole of your composite switch can be connected to the load.

The third relay if it were n.c contact could be used to reset the latch instead you will have to add another momentary n.c. switch to do that. You could use the third switch to invert the output. you would need to pullup the third coil using a resistor and then short that node to ground using the output of coil 2 (pole 2). This would waste power and get hot though depending on required coil current.

Do you follow or do you need a schematic?
Hi there,

Actually, you can build an RS flip flop Latch with only two relays.
I dont know if this will help the OP but here is a schematic...

Image
LEDs vs Bulbs, LEDs are winning.

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