Turn 6V motor on/off via 555 timer astable circuit and 5V relay

Thread Starter

Sw4n

Joined Dec 14, 2020
4
I have been working on a circuit to turn a motor on for several seconds, and then off for a longer period, using a 555 astable circuit. The on time needs to be around 5-10 seconds, and the off time needs to be about a minute. To get around the 50% duty cycle issue and allow for a longer off period, I put a signal switching 1N4148 diode across R2 of the timing control part of the astable circuit. I haven't tested this, and if anyone can see a glaring issue with what I have, input would be appreciated.
I then realised I might have another problem - this circuit is going to continuously drive the motor despite the timing, because the motor doesn't care about polarity. I came across the possibility of using a 5V relay coil to turn the motor on/off based on the drive circuit transistor coming from the 555 timer output I already had, but I am unsure how I connect the motor to this to achieve what I want, as most online examples show the motor having its own separate power supply, which I cannot do as the motor needs to be powered by the same supply as the 555 timer circuit. Basically, how do I get the motor to turn on and off using the timer circuit I have, and if I need the relay, how do I connect it with the 6V motor? My diagram is below. I have limited and rusty knowledge of circuit design, so explanations would be appreciated.
 

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ElectricSpidey

Joined Dec 2, 2017
1,449
Looks ok to me.

The alternative to using the diode would be to drive the motor with a PNP, since the cap charges thru both resistors but discharges only thru R2 (the lower resistor in the RC network). This reverses the logic and using a higher value for R2 will give you a longer off time than on.

But, I understand low side switching is sometimes preferred.

" I then realised I might have another problem - this circuit is going to continuously drive the motor despite the timing, because the motor doesn't care about polarity. "

This I don't understand...A 555 does not reverse polarity like a H-bridge.
 
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Thread Starter

Sw4n

Joined Dec 14, 2020
4
Looks ok to me.

The alternative to using the diode would be to drive the motor with a PNP, since the cap charges thru both resistors but discharges only thru R2 (the lower resistor in the RC network). This reverses the logic and using a higher value for R2 will give you a longer off time than on.

But, I understand low side switching is sometimes preferred.

" I then realised I might have another problem - this circuit is going to continuously drive the motor despite the timing, because the motor doesn't care about polarity. "

This I don't understand...A 555 does not reverse polarity like a half bridge.
I am trying to work with what electronics I already have access to, and I only have NPN transistors, so low side switching is preferred for that reason, but thank you for the suggestion.
This may be a misunderstanding on my part, I have struggled to find examples for what I am doing and have only found examples for other outputs like sensors or of using a similar circuit for motor speed control, not on/off motor control, and mentions that a motor will not work the same way as an LED/diode would in combination with an astable 555 circuit in turning on and off due to polarity - which is what got me confused and looking at relays. I have only ever worked with motors once before in a h-bridge set-up, so I'm not very familiar with them other than that changing voltage changes speed.
 

AlbertHall

Joined Jun 4, 2014
10,882
If it's like this one it needs 500mA to 2000mA, so you can't drive it directly from the '555
This shows how to connect the relay, motor and 6V suppply.
You might also replace the 1k, transistor, and relay with a MOSFET.
 

Thread Starter

Sw4n

Joined Dec 14, 2020
4
If it's like this one it needs 500mA to 2000mA, so you can't drive it directly from the '555
This shows how to connect the relay, motor and 6V suppply.
You might also replace the 1k, transistor, and relay with a MOSFET.
Thank you, I was unsure how to connect the relay to the motor and have it powered via the 6V supply, the circuit helps. Am I likely to have supply issues using a 6V supply with the relay and motor?

For the relay, am I looking at a 5V SPST coil relay similar to this?
https://www.amazon.co.uk/gp/product..._title_dp_1?ie=UTF8&psc=1&smid=A2AK1C4P3VJC4P

I did see that I could replace this part of the circuit with a MOSFET, but I am less familiar with them and do not have any to hand.
 

AlbertHall

Joined Jun 4, 2014
10,882
Am I likely to have supply issues using a 6V supply with the relay and motor?
You will probably need some decoupling on the supply to the '555 circuit otherwise it might go bonkers (technical term) with interference from the motor. Put a 100nF and 100uF capacitors as close to the '555 supply pins as you can. If there is still interference, increase the 100uF. Your supply should be capable of supplying 2A depending on the motor load.
 

eetech00

Joined Jun 8, 2013
2,274
I have been working on a circuit to turn a motor on for several seconds, and then off for a longer period, using a 555 astable circuit. The on time needs to be around 5-10 seconds, and the off time needs to be about a minute. To get around the 50% duty cycle issue and allow for a longer off period, I put a signal switching 1N4148 diode across R2 of the timing control part of the astable circuit. I haven't tested this, and if anyone can see a glaring issue with what I have, input would be appreciated.
I then realised I might have another problem - this circuit is going to continuously drive the motor despite the timing, because the motor doesn't care about polarity. I came across the possibility of using a 5V relay coil to turn the motor on/off based on the drive circuit transistor coming from the 555 timer output I already had, but I am unsure how I connect the motor to this to achieve what I want, as most online examples show the motor having its own separate power supply, which I cannot do as the motor needs to be powered by the same supply as the 555 timer circuit. Basically, how do I get the motor to turn on and off using the timer circuit I have, and if I need the relay, how do I connect it with the 6V motor? My diagram is below. I have limited and rusty knowledge of circuit design, so explanations would be appreciated.
You can also do it this way
you can set the timing without the diode.

1610936170756.png
 
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MisterBill2

Joined Jan 23, 2018
7,956
There is no need to use a relay, especially if you use that first circuit posted since the transistor will only be on or off and so there is no chance of reversing the motor power feed's polarity. And even driving it with the 555 directly, it can only run in one direction, unless the current through the LED is enough to run the motor.
 
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