http://www.scottpages.net/LilPulserSiliconChipTrainController-ckt.png
I have try to implement this circuit using a small 6V motor, i have only implement the voltage control and haven't tried the current circuit.
for applied voltage of 6V, with the motor rotating the line label Back emf i have obtain only 0.4V the reading is taken before it is halved. is it really the back emf value. Something that i am thinking is that the applied voltage is 6V- the back emf= 0.4V.
With an applied voltage of 4.5 the motor was barely moving and the back emf was 3.6V.
is this a plausible solution?
thanks

 

Your link doesn't work.

 

Link works find your browser may be old and can't display png images.

The two steering diodes D4 and D5 are sending both positive and negative (depending on motor direction at time of switch) emf through a voltage divider and filter which then shows up as a smoothed out dc signal at an opamp. After that I have no idea.


Original article which details theory of operation but it's pay to read. I think that's their circuit you have. http://www.siliconchip.com.au/cms/A_101082/article.html

Different designs without feedback that I can tell.
http://solorb.com/elect/pwm/pwm0/
http://solorb.com/elect/pwm/pwm1/index.html

 

http://www.scottpages.net/LilPulserSiliconChipTrainController-ckt.png
I have try to implement this circuit using a small 6V motor, i have only implement the voltage control and haven't tried the current circuit.
for applied voltage of 6V, with the motor rotating the line label Back emf i have obtain only 0.4V the reading is taken before it is halved. is it really the back emf value. Something that i am thinking is that the applied voltage is 6V- the back emf= 0.4V.
With an applied voltage of 4.5 the motor was barely moving and the back emf was 3.6V.
is this a plausible solution?
thanks

how you measure the back emf ?

 

using a CRO between D4 and D5, voltmeter also give the same reading

 

Junction between D4 and D5 is voltage at Q1 drain. Subtract this value from your supply to calculate voltage across the motor. If your CRO shows this as a DC value instead of pulses, Q1 is not turning off.