555 timings

scrawny git said:

Originally posted this yesterday in the 555 timer tutorial thread below, but no response.

I have built the circuit shown in the attachment to automate the on/off for a 24V motor - works fine, but now I need to adjust the timings. I have been playing around with different value resistors at R1 and R2 to do this but whatever I do I can't manage to get a big discrepancy between the on time (t1) and off time (t2).

Ideally what I want is for t2 to be at least five times the length of t1, so if it's on for about 1 second, it's then off for say five or six, perhaps even ten. I have had a look at the timing calculator linked in the other thread and no matter what values I input I can't get such a wide discrepancy. Any ideas?

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scrawny git said:

Thanks.

Right, apologies for my ignorance (i never learnt lectronix) but

the only diode i've got to hand is the rectifier diode I used on the other side of this circuit (IN4003) which I'm assuming is a bit much for this and that I would be better off with a simpler signal diode, say IN4148, right? wrong?

and you've put in a variable resistor: what sort of value does this need?

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ericgibbs said:

a little experimentation will be required...

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scrawny git said:

Originally posted this yesterday in the 555 timer tutorial thread below, but no response.

I have built the circuit shown in the attachment to automate the on/off for a 24V motor - works fine, but now I need to adjust the timings. I have been playing around with different value resistors at R1 and R2 to do this but whatever I do I can't manage to get a big discrepancy between the on time (t1) and off time (t2).

Ideally what I want is for t2 to be at least five times the length of t1, so if it's on for about 1 second, it's then off for say five or six, perhaps even ten. I have had a look at the timing calculator linked in the other thread and no matter what values I input I can't get such a wide discrepancy. Any ideas?

Click to expand...

Hero999 said:

Increasing the voltage on pin 5 also helps to increase the delay, for example, set it to 86.5% of the supply and you'll get double the RC time constant.

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