Does anyone know where to find a timer switch that upon activation from a momentary on will supply switched power for a predetermined time, then switch itself off?
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Generic timer switch?
- Thread starter 338_MtRushmore
- Start date
A 555 timer chip wired in monostable mode (if the time duration does not need to be extremely precise or very long).
I usually want to control a relay or solenoid for 120v. Just random projects that aren't radio related. Seems like there would be some sort of premade controller for a function so basic.
a common way to do something like this would be to use a latching relay setup.
here is a link where you can start learning about them:
www.morssmitt.com
in the most basic sense, once the coil of the relay gets a pulse of a certain polarity, it energizes the coil and it holds there until a pulse of the opposite polarity is applied.
LC
here is a link where you can start learning about them:
Latching relays - Mors Smitt railway components & solutions
Mors Smitt is designer and manufacturer of latching relays for high power railway applications.
in the most basic sense, once the coil of the relay gets a pulse of a certain polarity, it energizes the coil and it holds there until a pulse of the opposite polarity is applied.
LC
The relay isn't a huge problem, it's the timer to shut it off that is my problem.a common way to do something like this would be to use a latching relay setup.
here is a link where you can start learning about them:
Latching relays - Mors Smitt railway components & solutions
Mors Smitt is designer and manufacturer of latching relays for high power railway applications.
in the most basic sense, once the coil of the relay gets a pulse of a certain polarity, it energizes the coil and it holds there until a pulse of the opposite polarity is applied.
LC
Built something like this into a portable AM/FM radio decades ago. Was for my younger daughter, around age five. In the hands of a child the battery usually lasts until the first time the youngster walks away from it turned on. Just plays until the battery is exhausted. Found the circuit in a magazine. Had a NPN transistor in line with the positive battery lead. A CMOS hex inverter like a 74C14 had all six sections wired in parallel, connected to the transistor's base lead. This gave the transistor more drive current. When the chip's output pins were high, the radio would play. The chip's inputs had an electrolytic capacitor to ground, a 10 megohm resistor to the battery + voltage. So long as the capacitor was charged up, the chip inputs were high. Output pins would be low, and the NPN transistor turned off. The last component was a momentary normally-open pushbutton switch. It was wired in parallel with the electrolytic cap. Pushing the button shorted the cap to zero Volts. Ouput went to full high voltage, turning on the transistor. The 10 meg resistor would slowly charge it up. When the capacitor voltage reached the chip's input threshold, the outputs would fall back to zero and shut off the radio. Seems to me a 100uf cap was good for about ten minutes. Seemed like a believable attention span for a five-year old. The CMOS chip draws practically no current in the "off" state.
Worked as intended. The batteries lasted for weeks. Until the first time it fell face down. This kept the pushbutton closed, and ran down the battery.
Hadn't thought of that. Two weeks was still better than two days.
73
Worked as intended. The batteries lasted for weeks. Until the first time it fell face down. This kept the pushbutton closed, and ran down the battery.
Hadn't thought of that. Two weeks was still better than two days.
73
there's always one of these LOL:
Hyper Tough Heavy Duty Indoor Grounded Timer 15 Amp 39208223393 | eBay
1875W Resistive.
www.ebay.com
Mt R. -
You didn't mention if you wanted to switch 110vac or 12 v dc, If you want to switch 110, this one worked for me. From Amazon. There are others of same brand with different timeouts. Big button on the timer is push on - push off.
Amazon product ASIN B00IB0ZJXE
- 399
You didn't mention if you wanted to switch 110vac or 12 v dc, If you want to switch 110, this one worked for me. From Amazon. There are others of same brand with different timeouts. Big button on the timer is push on - push off.
Amazon product ASIN B00IB0ZJXE
- 399
Thanks once again nomad. It's almost too simple, but I'm glad I finally understand a circuit you posted
You need to use a 'true off-delay' timer, that is available 'off-the-shelf'.
Here's the schematic.
When the push button switch is momentarily actuated, the timer contact closes and the load is energised.
The load is de-energised when the timer contact opens after the set time has elapsed.
'True off-delay' timers are available with various operating voltages.
Nandu.
Here's the schematic.
When the push button switch is momentarily actuated, the timer contact closes and the load is energised.
The load is de-energised when the timer contact opens after the set time has elapsed.
'True off-delay' timers are available with various operating voltages.
Nandu.
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