Some questions need asking first.
1. What is attached to this motor and is there any possibility, no
matter how remote, that turning it on might cause harm to someone?
2. What motor environment monitoring are we being offered (end-limit
switches, speed of rotation sensor, torque sensors, motor current
monitor, motor temperature etc.).
3. Would you have a contactor mounted in a suitable enclosure with
the appropriate motor overload trips and isolators?
4. How big is the motor? (can't be too big if it runs from single
5. Have you produced a full risk assessment and would you care to
send me a copy to check over (for the appropriate fee of course ;>).
There will be other questions.
Essentially, controlling motor driven equipment from a PC is not
usually a very good idea. You can still use the PC as part of the MMI
but you need some means to mitigate risk should you get a software
hang-up or other problems communicating with the motor controller.
Some more details and plenty of us here can begin to provide more
Paul E. Bennett ....................<email:// email@example.com>
for a circuit idea see: http://www.geekinventions.com/downloads/k74.pdf
But first consider safety:
Make sure you have a manual isolator and an emergency stop (latching
pushbutton, twist to release) for the motor (in the motor relay or contactor
coil supply line). The motor should be protected with thermal overload or
fuses to prevent fires. If you don't know how to protect your circuit
safely you shouldn't be doing this.
Provide mechanical barries to keep people and animals away from live voltage
and moving parts. e.g. box it. Cage it. these are to prevent electrocution
and mangling. Enusre you comply with relevant earthing regulations.
You have to comply with all local health and safety laws.
Never work on a live system. Never work alone where there is risk of
Isolate your pc from the relay driver circuit as far as practical. There
are opto-isolator chips specifically designed to drive relays from ttl (5v).
Don't draw power from the PC to energise the relay(s). Use small relays to
switch bigger relays or contactors. all circuitry should be protected with
MCBs and/or fuses as appropriate. All cables must be rated to carry
Do install a watch dog circuit. for example: If the software on the PC
does't trigger the watch dog every 50 ms the watch dog trips out and removes
power to the relay board (if that is a safe way to shut down). You have to
design the circuit so that it shuts down safely.
You are responsible for your actions. If in doubt take training courses to
cover electrical safety, mechanical safety etc.
You have to buy a motor, and its driver, and a PC board for controlling the
You can program to control the motor with Borland C++ or else.
One example of a PC board may be the MEI motion controller.
There are various options for you. Check it.
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