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PC based speed control of DC Motor
We are doing a project related to PC based speed control of 1/2 HP DC Motor using Type - A chopper (MOSfet).
By K.V.N. Murali Mohan on 19 November, 2004 - 4:10 pm


We are doing a project related to PC based speed control of 1/2 HP DC Motor using Type - A chopper (MOSfet). The control circuit we use contains PC Parallel port, Hex buffer (7404), optocoupler (MCT2e) and Nand gate (4093). The output from nand is given to gate of Mosfet which is connected in series with DC Motor. The control logic is good if voltages are checked. The Power circuit is also working well when Mosfet is made On/Off. But when both the circuits are clubbed, the Not gate is blowing up and parallel port pin which is used for control is always high irrespective of value sent to it. The program is written in C language.

The main problem is rised at neutral (ground point). It is blowing up first as and when 220V supply is given to motor. Please give us necessary guidance to the above problem.


Hi man;

It looks like the old grimlin lol...
Well, here is the likely problem...
The PC ground is almost never at true ground; it's usually something around two volts or so... The 220 volts supply has it's own ground, therefore when the two are interconnected, a large amount of current is shunted through very little resistance. Result, blow out.

You do mention the opto coupler, make sure it's correctly wired. As to a possible solutions, you must keep the two grounds apart from each other...

Walt Njuh
Akumeka Tech

By vivek.n.i.t. jamshedpur on 18 January, 2005 - 11:36 pm


this is vivek

i am donig a project on the same topic as mentioned above. the thing is that i have got a control circuit for small value motor, i need for a large rating as the people have done using mosfet. so please can u give the references of that project? plesae give me some web adress and some references.

thank you.

hello sir,
i am naveen. i am also doing the same project, but we are using 'DECDOER& 555 TIMER CIRCUIT' by using that electronic components we are doing the our project work . but we are not satisfy with that one, we need to do some better application for it.

i request you to suggest me a better applicaton for my project & send the the data abt that application to my id

thank you sir

Call me at
07172- 276418
- 225231


i am doing a project on pc based speed control of dc motor using PWM technique. we are using 'DECDOER& 555 TIMER CIRCUIT' for the control circuit. I'm in need of some better application for it. The motor used is of small rating. if i want to use a higher rating one, can anyone suggest me what driver circuit i should use and also how to design/choose these driver circuits?

if posible pls send the circuit schematic available it's urgent.

pls frwd it on
thank you.