PWM output to control pumps

[SKL BOI]

Hi
I am trying to create a pump controller that will increase in speed when a temperature sensor increases in temperature!
I want to do it using the PWM output.
I have the David Lincon customizing and programing PICAXE controller book and im going from the motor control circuit in it on page 246 attatched is a circuit diagram that i have made of the circuit that i think will work can you tell me if that circuit will work if i get the programing rite ive been trying so many methods to make this work and have recently gone onto this PWM idea so its my last hope!
If this will not work can you please tell me how to make it work! thanks

SKL BOI

 

[hippy]

You have the thermistor connected to Output Pin 0 ( leg 7 ), that is not correct. You should connect it to Pin 1 ( leg 6 ) which can be used with READADC.

The 1K balancing the thermistor as a potential divider may need to be changed depending upon what range of resistances that thermistor has but it should probably be good enough to do some testing.

 

[SKL BOI]

Hi
Thank you very much for the quick responce ive made those changes and ill do a test bed and change the resisters until it works correctly!

Thanks again

 

[Dippy]

Best to let everyone know what sort of motor is used in pump.
Is it a little DC motor with brushes?
Have you selected the correct transistor and base resistor for the job?
This is where experimentation can be informative.

A lot of people recommend a little capacitor across motor brushes if brush type.

Also, depending on the nitty-gritty of the power supply, it is usually recommended to have a decoupling capacitor on the PICAXE power pins - to reduce any sparklies getting to PICAXE.

Also, to be safer, make your ground returns for motor and PICAXE separate. i.e. take the motor ground back to power supply and a separate ground return from your PICAXE so that motor current doesn't flow through ground line from PICAXE. (If that makes any sense).
It may be OK with a baby motor and fat grounds but it's good practice to keep grounds separate.

 

[hippy]

Take a bit of time to wait to see if there are other issues people pick up on as I haven't considered everything there ( I know little about PWM driving of motors with transistors ).

You'll likely want to add some 100nF decoupling capacitors aroud the circuit to make it more immune to radiated interference from the motor and PWM switching.