Bi-directional Motor with speed control circuit

[Stoneww]

Hello I'm trying to make a circuit to make a motor spin in both directions and so that I can alter its speed.

>The blue rectangle is the part of the circuit for the bi-directional control. The blue rectangle circuit works prefect on its own

>The green rectangle circuit is used to alter the speed of the motor. (A slightly different model of this circuited worked perfectly standalone).

Now the design I've tried below only lets me control the speed of the motor in one direction and not in the other. Can someone please suggest how I can alter the circuit so I can control the speed of the motor in both directions? (Preferably without building a second 555 timer astable circuit, I want to try to keep to one but if this isn't possible then whatever comes to your mind!)

Thank you

 

[kellys_eye]

Use an 'h-bridge' arrangement and apply the speed controlling signal to the appropriate motor-controlled pair of transistors.

 

[Alec_t]

With Relay1 contacts as shown, the 555 supply is shorted to ground, so the 555 won't then function. Although the relay coils should connect to Vcc the contacts shouldn't. They should instead connect to the 555 output pin.
You should add reverse-biased diodes across the relay coils (unless they are internally provided in the relays) to protect the transistors from voltage spikes when the coils switch off.

 

[duke37]

Use a single two plole changeover relay to swap the motor leads over. When the relay is energised, the motor will run one way, when unenergised it will run the other way. This is an alternative to the H Bridge.
Using two relays means that you need circuitry to ensure that the motor is not asked to run both ways at once.

 

[Alec_t]

You could avoid relays altogether by using a double-pole ON-OFF-ON toggle switch.

 

[Stoneww]

I've managed to get it working perfectly with relays. I want to attempt the project using a H-channel, us there any advantage of using a H-channel over a relay configuration?

 

[Minder]

One of the advantages of H-bridge is the ability to PWM, also turn on the bottom devices for braking.
Otherwise, not that many.
M.

 

[duke37]

Relays will be bigger and possibly more expensive. They may have contact problems and may need fettling after 100,000 operations. They will be more robust if subjected to high voltage pulses but the 555 will likely fail first.