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

[seaneking]

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, 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 , 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

 

[Boncuk]

Hi Sean,

you forgot to give more details about the circuit you need.

1. Fixed time: seconds, minutes, hours?

2. Motor: AC or DC?, voltage and wattage?

Having those info I'll try to design a circuit (and PCB layout) for you.

Regards

Boncuk

 

[seaneking]

Awesome, thanks Boncuk!

Regarding your questions:

1. The time will be in the seconds range (don't know exactly how long yet, need some testing to determine that)

2. There will actually be two motors (they're both doing the exact same thing, same time, etc. that's why I didn't mention it earlier), DC, between 6-12v (I haven't sourced them yet, so not 100% sure). As for wattage, they'll be gearbox motors with a high gearing ratio (60rpm or slower speed-wise), so assume wattage is on the higher end of the scale.

Sorry for being so vague, I didn't really think I'd need specifics before designing the circuit (stupid me lol), if the info's just for part values, I can change that myself later, so don't worry too much.

Oh, and there's no need for a PCB layout as I need to make it free-form for the project I have in mind.


Thanks again,
Sean

 

[Boncuk]

Hi Sean,

I suppose electronics work requires some kind of precision.

If using geared motors of 6 to 12V supply voltage you'd more on the lower side of current demand than on the high side.

Also timings in the seconds range requires a bit more information.

Accurate timings > 60 seconds are hard to achieve using an NE555 timer circuit, since timing depends a lot on the timing capacitor with tolerances up to 40%.

For highest possible precision I do not recommend a timer IC, but go for a digital counter circuit with digitally preset times.

Can't help it! Germans tend to precise work.

Regards

Boncuk

 

[misterT]

Here is a circuit that can do the timing: 555 Monostable Multivibrator
And read this thread to learn how to switch the motor on and off using the output of the timer circuit: https://www.electro-tech-online.com/threads/how-to-switch-a-12v-line-through-a-fet.109591/

I think you can find a mechanical switch that can reverse the motor connection.. if you need more automated method for reversing the motor direction, you need to give more information about how you would like the user interface to function.

Look out for the limitations in the accuracy of the timing circuit and the power limits in the switching circuit.

 

[ajsivsan]

Simple. What ever your rating may be.. the whole process could be done using a single switch. First time you press the motor rotates in forward direction. The second time you press, it rotates in reverse direction. The state of the switch( active/ Wait) could be displayed via a LED. I can do this. Even i will create a schematic, PCB desgin for you.

This is my suggestion. Let me know if you are okay with this.
1. There will be one switch, two LED's( one for forward and another for reverse)

2. Initially, the forward LED will be active telling the user that if switch is pressed, the motor will turn forward. Once you press the switch, the motor will turn for lets say 5 seconds. Till that time no led will be active. Once the motor stops, the reverse led will be active indicating the switch will turn the motor in reverse direction.

I guess you understood my design.

 

[Boncuk]

I guess you understood my design.

I didn't understand it.

The OP wants the motor to run on a button push and stop it at any time (overriding the timer) using the same button. To reverse the motor it has to stop first. Using the same button for three functions requires some logic circuitry.

Boncuk

 

[ajsivsan]

I didn't understand it.

The OP wants the motor to run on a button push and stop it at any time (overriding the timer) using the same button. To reverse the motor it has to stop first. Using the same button for three functions requires some logic circuitry.

Boncuk

Forget it.... the requirement is without micorcontroller
So single button cant do anything

 

[seaneking]

First of all, thanks everyone for so much help so quickly!

The precision isn't a huge deal, it doesn't need millisecond precision, a second or two + - would be tolerable. Although, obviously precision isn't a bad thing either so if the digital counter circuit is more effective, and not that much more complex (read: expensive), and doesn't need any programming, then that may be the way to go.

I understand the 555 one shot circuit that MisterT suggested, but just a few questions. First, how could I prevent misfires, etc. after the first pulse of the output? Does it matter if the input (push switch signal in this case) is held open, say by a triac? then there could be a NC push switch to cut off power to the triac and 'reset' the circuit ready for it's next use/reversing the motors. Oh, but that 555 circuit wouldn't drain the batteries if the switch was held open would it?

Is there a simpler way to do this? maybe make the reset and reverse function one in the same?

And a mechanical switch to reverse the direction of the motors is fine, as long as they go for the same period of time in reverse as they went forwards. Also, I don't entirely understand how to apply the 555 circuit to control the motor. What is with the high-side and low-side circuits? Why couldn't the output just be directly connected to the motors? Am I missing something really obvious? (I assume so).

@ajsivsan, unfortunately the two switches (to start it and reverse it) need to be separate. And the triggering switch needs to be protected/held open, as it will be a noisy push switch signal that will probably cause misfires otherwise. Could the circuit you're thinking of accommodate for that?


Sorry there are so many questions, I'm trying my best to get my head around all this stuff! I think the 555 circuit would be the best bet (mainly because I sort of understand it ) as long as the precision thing is not too big of an issue. Now I just need to understand how to apply it to motor control, and incorporate the whole switch protection and reverse and stuff.

oh, and I've been thinking, I think the voltage would be more towards the 6v level, but it depends if I can get motors with high enough torque in that voltage.

 

[seaneking]

I don't need to stop the motor and override the timer, it was probably the way i worded it, sorry.

There's one push button that triggers the motor to turn for a set time. That switch may be accidentally pushed, held down, etc. throughout the runtime of the circuit (ie: it'll be a noisy signal), so it needs to be held open or otherwise protected from misfires. This switch will need to be 'enabled' (ie: circuit reset) before the next usage. Then there's another switch that reverses the motors for the same period of time. It would be nice (but not integral) if the reset and reverse switch could be one in the same thing.

 

[misterT]

The details are a bit vague to me. What do you (seaneking) mean by: "The switch, once pushed, needs to be 'deactivated' so that pushing it again wont trigger the motor to turn again"? Do you mean that if the motor has turned, say clockwise, then it wont turn to that same direction ever.. until it has turned to the other direction the same amount?

Could the application use limit-switches instead of timers? It would be much safer and more accurate.. assuming that the motor has to turn back and forth between two positions.

 

[ajsivsan]

The details are a bit vague to me. What do you (seaneking) mean by: "The switch, once pushed, needs to be 'deactivated' so that pushing it again wont trigger the motor to turn again"?

It means, lets assume the timer is 5 seconds. Your press the button and the motor runs for 5 seconds. Accidentally at the end of 4th second, if you press again another 5 seconds shouldn't be added to it. The switch should be disabled for 5 seconds after it is pressed.

 

[misterT]

It means, lets assume the timer is 5 seconds. Your press the button and the motor runs for 5 seconds. Accidentally at the end of 4th second, if you press again another 5 seconds shouldn't be added to it. The switch should be disabled for 5 seconds after it is pressed.

Yes, that feature was clear to me. But what about after the motor has been driven to one direction (for 5 seconds as in your example) and it has stopped? Should it be possible to do the same thing again (to drive the motor to the same direction the same amount of time).. or should that direction be disabled until the motor is driven backwards.. back to the original (starting) position?

 

[seaneking]

yes, that direction should be disabled until after the motor has been driven back to the starting position. I did write a big in-depth post responding to all your replies but since I'm new its still under moderation.

I don't have any experience with limit switches, i did a bit of googling, and sort of get how they work, but i don't know how to fit it all together and make it work. If they avoid the need of the timer, and keep it simple, then sounds good!

I might as well restate some of the stuff I said in my post that's under moderation (it'll probably pop up soon anyway). I like that 555 circuit you (MisterT) pointed me to, and I understand it (for a nice change). To stop the motors from triggering again and again, could you hold the push switch open with a triac to supply a continuous signal to the one shot? would that work? and then have a nc push switch to reset the triac, and then....um...somehow reverse the whole thing??

The only thing I don't get, is that post about how to apply it to control a motor. what's with the high and low side circuits? why can't you just connect the output straight to the motor...I guess I'm missing something really obvious.

 

[ajsivsan]

Here is a interesting link. Circuit Simulator Applet

This has a java applet to do the simulation online. Its really awesome.
Go to circuits --> 555 timer----> monostable multivibrator. There try to press the trigger. That is where you should place your switch. Initially the output voltage will be 0V. Once you press the trigger, the voltage is 5V. You can see the wave form too.. also in the mean time how many times you press the button doesn't change the timining and output. I hope half of your requirment is done..

 

[seaneking]

thanks ajsivsan, but MisterT beat you to it, he already pointed me towards that site.