Need help with circuit, willing to pay for full design!

[seaneking1]

Hi everyone,

A bit of background first, I know only the basics of electronics (ie: I know what components do and how to read schematics), but have no idea how to design circuits, hence why I'm coming here for help.

Now to the (slightly odd) circuit.

- In essence I simply need to trigger a DC motor to turn for a fixed amount of time.

- The switch that triggers the motor will be a push switch that may be only pushed briefly (not held down 100% of the time). The switch, once pushed, needs to be 'deactivated' so that pushing it again wont trigger the motor to turn again. I assume it then needs some sort of 'reset' button to activate the switch again?

- Also (yes, there's more) I need another switch that will reverse the direction of the motor so that it turns backwards for the same amount of time it was set to turn forwards in the first place. (no need for the whole deactivation/trip protection in this one)

- If the reset switch and reverse switch could somehow be one in the same thing it would be awesome, but really doesn't matter that much if I use two separate switches (so three in total)


I was thinking a 555 timer to control the whole motor timing thing, and a triac to control the whole switch re-trip protection/one push triggering thing. How (or if) it could all fit together I have no idea. I would like to keep it as simple as possible, and I don't have the tools (or budget) to program anything on a microcontroller. I realize that I'm asking a lot, and of course I would love some free advice;D, but if someone is willing to design the whole circuit (schematic and all), then i would also be willing to pay (via paypal).

So, any ideas?

oh, and feel free to pm me if you'd be willing to design it for me/give me a quote.


Thanks!
Sean

 

[seaneking1]

Anyone? Anyone at all?  ???

I've been doing some googling and asking around, and I've come up with half of the circuit so far:

It uses a monostable multivibrator for the single timed pulse (controlled through the pot), and a triac to hold SW1 open so that repeated firings do not create more pulses. SW2 cuts power to the triac and resets the circuit.

Would that work? Would the triac drain the battery or something?

Only thing is that I have no idea how to make the pulse from the one shot control the motor.  And as you can see, I haven't finished the circuit. I don't know how to reverse the motor so that it turns back to the starting position. And I would really like to make the reset and reverse switch one in the same thing.

 

[Hero999]

That circuit won't work. It's not a TRAIC, it's an SCR which is connected backwards and pin 2 of the 555 has no pull-up.

It's pretty easy to make a monostable which is triggered by pressing a switch and is not retriggerable, using the standard 555 timer circuit and an AC coupling capacitor, the circuit is on the 555 timer's data sheet which can be found using Google.

What do you mean by the reset switch?

Adding a reset to a 555 timer causes the timing cycle to terminate when it's pushed.

A 555 timer can't power a motor directly, you need to add a booster transistor to drive the motor.

The direction of the motor can be reversed using a DPDT switch, which is a type of toggle switch: one position for forward and the other for backward. If you want a momentary switch to cause the direction to alternate between forward and backward, it's possible but more complicated because it needs a transistor h-bridge and a flip-flop. Does the motor have to be stopped before it's put into reverse? If it's a large motor, its not a good idea to reverse it whist it's spinning, at least not too often.

What size is the motor? How much current does it draw? What voltage is the power supply?

How long does the delay need to last for?

What's it for? It's possible you're doing this the hard way.