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Old 3rd January 2015, 06:43 PM   #1
hoihen is offline hoihen  Netherlands
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Default Delay circuit, more delay time needed

Hello,

Iím using the small circuit below to delay a relay. The circuit 5V input of the circuit is delayed and then fed as trigger to a relay circuit.

The setup below doesnít allow enough delay, so I updated the C1 capacitor to 470uF, now Iím only a second or two short of what I need.

The person I got this circuit from indicated that I should not use more than 470uF, I expect this is due the current flowing through the resistor.

Is there an easy way to add the 1-2 seconds delay?

Thanks and regards,

HJH
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Old 3rd January 2015, 07:05 PM   #2
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Increase the value of R1. You may or may not need to increase R2 as well.

Mike
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Old 3rd January 2015, 07:22 PM   #3
hoihen is offline hoihen  Netherlands
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Thx, I will try.

If I understand correctly it's not only possible to change the delay by adding more capacitance, but also slowing the charging by increasing the R value?

HJH
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Old 3rd January 2015, 07:45 PM   #4
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You can increase the value of the C1 to infinity if you like.
The current in R1 is negligible.
You might want to change the Q1 to BD139 though, or something like...
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Old 3rd January 2015, 08:14 PM   #5
hoihen is offline hoihen  Netherlands
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I'm not sure if I understand you correctly. The BD139 is a transistor capable of a higher current.

You expect the current through the BC547C could be problematic?
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Old 3rd January 2015, 08:27 PM   #6
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Use a 555 timer. The sky is your limit, one can arrange a turn off point for powering down etc.
555 timer
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Old 3rd January 2015, 08:51 PM   #7
hoihen is offline hoihen  Netherlands
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Thx. A timer IC would be a good idea, but I'm unfortunately not that schooled in electronics to develop a complete circuit myself.

If there are some basic and easy schematics that would help.
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Old 4th January 2015, 08:19 AM   #8
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Quote:
Originally Posted by hoihen View Post
I'm not sure if I understand you correctly. The BD139 is a transistor capable of a higher current.

You expect the current through the BC547C could be problematic?
One more vote for a 555 from me.
Definitely worth learning.
I control pretty much everything in a power supply with those. Delays, relay driving, voltage monitoring,... oscillators... You name it...

Anyways,
to design a simple one transistor delay circuit, we might want to have a bit more information about your actual relay itself.
For example, what is its coil resistance?
And what is the minimum switch on voltage of it?
Measure them, if not available from the data sheets.
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Old 4th January 2015, 08:47 AM   #9
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by hoihen View Post
Thx. A timer IC would be a good idea, but I'm unfortunately not that schooled in electronics to develop a complete circuit myself.
Increase C1. There is no reason why it can't be larger than 470uF. Also, if you show use some more of the circuit (exactly what happens after the transistor?) we may be able to help even more.
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Old 4th January 2015, 08:58 AM   #10
Mooly is offline Mooly  United Kingdom
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If its just a clean 0 to 5 volt trigger signal that is needed then CMOS gate (schmitt trigger) would be perfect. One IC, one resistor and one (tiny) cap.
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