relay circuit

Several ways. One is to use some 555 timmers in each switch to give a 1 second delay. Then use an extra set of contacts onthe relay to go fro the coil to the power supply. Put another normally closed switch in that line to break the power and reset the relay. See any standard 3 wire motor starter circuit.

If the relays draw a small ammount of current, go from the power source to the switch then put a large value resistor in series and a capacitor across the coil. When the capacitor charges the relay will pull in. To seal it in, see above.

_ / \ GND-(- +)o--o--------------o------------o \_/ >| | 2N2907 |-o-o | 12V /| | | | | | | | | .-. | | 10k | | o | | | .o.10k | \ '-' | | | o o | | | o)| 220 Schottky diode o '-' )| ___ | | _)| OFF (Grd) oo|___|--| 220k | | o | --- === 100uf --- GND | | === GND (created by AACircuit v1.28.6 beta 04/19/05

e been made for >1sec or the relay will not operate.

circuit

use a stupid microcontroller. It would be less than 100 lines of C code.

Bye Jack

"use a stupid microcontroller. It would be less than 100 lines of C code. "

...and about 1/10 the price.

f 3 momentary switches and then operate a relay.

ave been made for >1sec or the relay will not operate.

e circuit

if it's a one time thing, probably buying an Arduino and some shield with c onnectors and relays will not be the cheaper solution, but definitely the f aster.

Bye Jack

A PIC16F690, 5v reg, a transistor, some vector board. Or $5.25 Arduino from Ebay & a transistor.

A real minimalist dodge is the unijunction transistor.

They're probably getting hard to find - next in line is the programmable unijunction transistor, which is basically a thyristor with the gate at the wrong end.

The PUT is also getting rare these days, but the complementary assymetry of the 4-layer device means you can turn the circuit upside down and use a low power SCR like the 2N5061.

You need a bleed resistor across the timing capacitor to leak the charge away when the button isn't pressed, the circuit produces a narrow pulse suitable for tripping a latch.

using a SCR is the simplest thing to do... Put NC switch in series with it to open the circuit. a NO switch to apply some gate current with a RC network to get a delay on.

Senstive SCR's work well for pulling in a relay coil ...

Essentially; the SCR variant of the PUT circuit I suggested is exactly that - but its applied more intelligently to get repeatable, predictable delay period.