Help in wiper motor circuit

[venktech]

I m planning to construct a wiper for my helmet.. I have chosen 100 rpm gear motor for this and the mechanism would be like the motor should change the direction periodically (every 2 seconds)..

I built a circuit using 2N3904 transistors for switching the current but the output current is not sufficient.. is there any compact circuit like a single IC which will reverse the current for every 2 sec and give high current upto 1 A...? I would like the circuit to be very compact..

 

[poor mystic]

Hi Venktech
The circuit you want is called an 'H-bridge'. An example of a single package H-bridge is the LMD 18200 http://www.national.com/mpf/LM/LMD18200.html which is rated for 3A continuous and 55V.
Your local supplier may have alternative packages.

 

[venktech]

Thank you... But this is a motor driver which requires a signal or a pwm from a microcontrolller for changing the direction of the motor right?.. is there any other ic which would automatically reverse output dc current periodically without any signal?

 

[Resqueline]

Do you really think the motor will run exactly the same length for every sweep back & forth? Think again, it wont, it'll creep up-up-&-away with every sweep.
There's no way you can set a timing only and expect it to remain in position. You will need end-stops (crude/brutal) or end-of-travel switches to signal a reversal.

 

[venktech]

Do you really think the motor will run exactly the same length for every sweep back & forth? Think again, it wont, it'll creep up-up-&-away with every sweep.
There's no way you can set a timing only and expect it to remain in position. You will need end-stops (crude/brutal) or end-of-travel switches to signal a reversal.

Yeah.. I do agree.. We can set a stopper or something to stop at the maximum height..But how can i generate an alternating DC current (ie dc current whch reverses fr evry 2 sec)...?

 

[poor mystic]

The IC has a logical direction pin which is given a voltage to reverse the motor. Perhaps an RC network would help - you could have the RC network charge to reverse direction once C reached the control voltage and discharge once voltages are reversed. There should be some imaginative way to get a bit of hysterisis in there to make switching reliable.

 

[poor mystic]

... though now that Resquiline has pointed out what he has, I don't like the RC network at all. I'd look for a mechanical solution first.
Perhaps a slotted wheel which is rotated first this way, then that, with an opto-interrupter looking through the slot. A few degrees of lag in the movement of the slotted wheel would provide the needed hysterisis.

 

[venktech]

I find lil diff to visualize what you are trying to say.. i hope that u r saying to do something mechanically to obtain the reversed direction instead of electronic way...

 

[duke37]

A simple oscillator can be made with a cmos Scmitt NAND gate (4093). With a capacitor to ground on the input and a resistor fom output to input, a frequency of oscillation is 2.7/(R*C).
For a frequency of 0.25 and 100uF cap you will need a resistor of 110k. The output should go to the H bridge direction terminal. Unused gates should have their inputs connected to ground.
Stalling the motor at the end of the stroke would seem to me to be a recipe for disaster.

 

[venktech]

A simple oscillator can be made with a cmos Scmitt NAND gate (4093). With a capacitor to ground on the input and a resistor fom output to input, a frequency of oscillation is 2.7/(R*C).
For a frequency of 0.25 and 100uF cap you will need a resistor of 110k. The output should go to the H bridge direction terminal. Unused gates should have their inputs connected to ground.
Stalling the motor at the end of the stroke would seem to me to be a recipe for disaster.

Good idea.. even i was thinking abt giving the square wave to the motor driver shield... what abt astable multivibrator with a transistor.. ? and will the circuit look compact?

 

[poor mystic]

I thought we had accepted that the astable (free-running multivibrator) was not the way to go?

BTW Yes, I have thought of an opto-mechanical solution but what a*&^%^ of a draughting job.

 

[poor mystic]

Stalling the motor at the end of the stroke would seem to me to be a recipe for disaster.

I had thought that you might use the wiper mechanism to operate a switch which would hold in its bistable position until once again reversed by the next half-stroke.

 

[TBennettcc]

What about a typical wiper motor linkage?

The motor runs in one direction. There is an arm attached to the motor. This arm is attached to another arm by a pivot. The second arm is inside a sleeve. The wiper is attached to both the sleeve and the arm inside. As the motor spins around, the rotational movement is translated into linear movement, which moves the motor back and forth. The distance 'd' of the attachment point to the motor, from the center spindle of the motor, determines the distance the wiper travels.

(Please excuse the rather unpolished diagram, but you get the idea.)