I need two special types of relays (for lack of a better word) for a project :
1> Relay #1 - Changes position (i.e. if it was OFF it goes to ON and if it was ON it goes to OFF) when the primary receives a current (I have 110 V ON-OFF Signal - but I can convert that to DC if necessary). It should NOT change position when there is no signal. I am trying to illustrate this as follows (t is time in minutes ):
t < 0, No Primary Signal, Switch is in OFF position
0<t<t1, Primary Signal, Switch is in ON position
t1<t<t2, No Primary Signal, Swith is in ON position
t2<t<t2+t1, Primary Signal, Switch is in OFF position
t2+t1<t<t2+t1+t2, No Primary Signal, Switch is in OFF position
t1 is expected to be around 1-3 mins. and t2 is expected to be 5-10 mins. The load for the Switch is 110V, 0.5 amps.
Is there any OFF the shelf device which will do this ? Or is there a simple way of making one ?
2> Relay #2 - This Relay powers up with a delay which can be preset from 1-5 mins.
Is there any off the shelf devices which will do this ? Or is there a simple way of making one ? I need something which is reliable too.
Sournds like you need a latching relay for #1. Solid state time delay units are available. Allied Radio or Radio Shack would be the place to look for both of them.
I would probably do it with a small microcontroller like a PIC controlling a couple of relays via a fairly simply driver circuit. The reason for using the PIC is that you can add some software filtering for relay #1 to make sure it doesn’t glitch and go through multiple ON-OFF-ON-OFF cycles from a single normal command cycle. Also, you can get very accurate variable time delays from a PIC, which would make the control of relay #2 very easy.
A latching relay would be the best. And if you can’t find one of those, you can build a latching relay circuit out of at most 4 standard relays. I can draw up a schematic for you if you want.
I wouldn’t recommend doing it with a MCU, unless you want to buy the nessecary hardware and software and be prepared to learn how to write your own code. For a simple task like this a relay solution will be easier to implement and maintain and more reliable.
I like the latching relay (thanks David Simmons and Andrew). I am looking at the latching relays from McMaster (http://www.mcmaster.com/catalog/108/html/0800.html).
However, it says the relays work with momentary signals (the signal i’m looking for will last for like a minute). Will it work with that ?
Also, Andrew can you please give me the schematic?