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Help Garaged Time Delayed Switch

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health

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Got this schematic consisting of 2 LM 555. 1 relay which is named Power On Delay Circuit with Flashing/Solid Indicator LED. I want to build a switch which will close my garage door itself after a certain time, like three minutes or more, should I forget to close it.

I would be gratgeful for help on the values of R1's and C1's which are not given. I would also be grateful for advice on other similar schematics for this usage.
 

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Hi health,

for this long time period you must choose a CMOS version of the timer circuit (TLC7555).

For part A (monostable) select 1.5MΩ for R1 and 100µF for C1. This will give a time delay of 164 seconds.

For part B (astable, flashing LED) select 270KΩ for R1, 560KΩ for R2 (misprint in the schematic, both labelled R1). R2 is the resistor between pins 6 and 7. For C1 select 1µF. The flashing frequency will be 1.038Hz at a duty cycle of ~60%, on time is longer than off time.

Do not use an NE555 for the circuit. It won't work for the monostable MVV.

To calculate the current limiting resistor for the LED use this formula: RV=(+UB-UF)/IF, where +UB is the supply voltage, UF is LED forward voltage (1.8V for red, 2.4V for green and orange), IF is the LED forward current (normally 20mA). In the calculation use voltage in V, current in A.

Boncuk
 
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Hi Boncuk,

Thanks very much for the reply.

In fact, I tried the circuit with 1k resistors and 0.1 uf capacitors and it didn't work.

As you mentioned, a cmos version is required. I can't get a TLC7555 from the local electronics store. They only carry 45xx and 40xx CMOS. Could any of these series be used to substitute TLC7555. If it could, can you please advice me on any changes required to be made to the circuit.

Best wishes.
 
Hi Boncuk,

Thanks very much for the reply.

In fact, I tried the circuit with 1k resistors and 0.1 uf capacitors and it didn't work.

As you mentioned, a cmos version is required. I can't get a TLC7555 from the local electronics store. They only carry 45xx and 40xx CMOS. Could any of these series be used to substitute TLC7555. If it could, can you please advice me on any changes required to be made to the circuit.

Best wishes.

hi,
If you can get CMOS dividers etc, one way would be to use a TTL 555 to give the longest reasonable timing as an astable and feed this into a 4024/40 CMOS divider ic. Pick off the delayed time from the divider, do the same for the 2nd stage.

Do you follow OK.?
 
Yoiu can also make a monostable from opamps and probably get better timing component values.
 
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