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Making a realy latch

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I had a look at the sites you posted. Any of the relays would suffice.

But I looked at the JayCar site and their prices are lower.

I'll leave it to you to decide. I just need to know the decisions.

I presume that SPCO means single pole change over which means SPDT.
 
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That transistor is OK & the cheaper relay will suffice.

I looked at the data sheets of both relays. SPCO is as I wrote in a previous post.

Diode cathode on 86 means there is an internal diode and its cathode is connected to pin 86.

Attached is the suggested circuit.

When the +5Volt supply is turned on, C1 is discharged, thus the FF is reset.

Q’ (Q bar) goes high at reset thus the transistor is turned on and the relay will operate.

C1 charges via R1 and removes the reset potential.

C1 will be fully charged after about 0.5 sec, so the FF is ready to receive an OP3 pulse.

When an OP3 pulse occurs, Q’ will go low, thus turning the transistor off hence the relay releases.

D1 reduces the back EMF to about 0.8 Volt (as measured at the coil terminals - internally it will be 12 Volt) thus protecting the transistor from destruction.

This relay needs an external diode as there is not one inside.

Feel free to ask any questions.
 

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Thanks Len. That is really great, and thanks for the explaination aswel, that helps alot!

The cheaper relay being the SPCO PCB mount part? Just to clarfiy.

Well its a bit late now but Im going to order the parts tommorrow. I cant wait to build it, especially to get this part of the circuit working :)

Thanks again
 
Thanks Len. That is really great, and thanks for the explaination aswel, that helps alot!

The cheaper relay being the SPCO PCB mount part? Just to clarfiy. Yes

Well its a bit late now but Im going to order the parts tommorrow. I cant wait to build it, especially to get this part of the circuit working :)

Thanks again
You're welcome.
As I said previously, based on a brief scan of the data sheet, I don't think you'll have a problem with OP3 spikes.

However, it is easy to filter the OP3 line if you do have a problem.

Spikes would cause apparent non toggling since an odd number of spikes (I think I foregot in the earlier post that the OP3 edge must also be counted) will result in an even number of toggles (hence mere humans would not see any change).

So you would only see a change if there is an even number of spikes.

The easiest way to detect the presence of spikes on a scope would be to put the scope on the Q or Q' output of the FF. It would difficult to see them on the OP3 line with a scope since they are likely to be very short.
 
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