Looking for a SMALL Motor Timed On Circuit

Thread Starter

george0039

Joined Oct 15, 2008
167
Hello
Hope the title is clear BUT if NOT, I need a small circuit in size, that will run a motor for a desired amount of seconds then stop and then can be Easily reset by the operator. The specs are:
1) Main power 3.7v 1s Lipo
2) Motor brushed 3.7v, 1A Max draw.
3) Circuit needs to run 10 seconds OR can be user adjusted 5-15 seconds, then stops.
4) Reset by user by way of a magnet, plan on using Reed switch N.C open-off with magnet, remove magnet then restarts motor run.
5) Circuit size, has to fit inside of 8mm dia. tube. Might be slightly larger.

Any help with the circuit design would be Greatly appreciated.
Thanks
George
 

LesJones

Joined Jan 8, 2017
2,687
I think the size constraint would require using surface mount components. I would suggest using an 8 pin microcontroller (Such as an ATtiny13 or PIC12F1840) An a small logic level power mosfet such as a FDS8896 as the switching device. If you need the adjustable version I can only think of a small preset potentiometer as a means of adjusting the time. (Fed into the ADC input of the microcontroller.) I can't think of any switch that would be small enough.

Les.
 

ArakelTheDragon

Joined Nov 18, 2016
1,350
I also suggest a PIC micro (definitely not arduino), you can use a digital pot (I2C, SPI interface) with PIC16F877A and the internal timer. Make a delay function with 1 sec time and then increase.it depending on the pot's position.
 

Bernard

Joined Aug 7, 2008
5,618
I would go dead bug, with a std. 555 as one-shot, timing cap 20 NP SM, motor driver NPN , FZT849, 80V, 7 A, B 100. Use small reed SW to trigger. All will fit in 8 mm tube.
 

MaxHeadRoom

Joined Jul 18, 2013
21,259
I would second the 12f series, many versions would do it.
If an external magnet is used to set on off, it could also be used to step a separate reed relay or hall sensor uni-polar, bi-polar or bi-polar latch, Honeywell SS400 series, min LED's to set time on.
How do you intend an indicator of time set?
Max.
 

Thread Starter

george0039

Joined Oct 15, 2008
167
I would second the 12f series, many versions would do it.
If an external magnet is used to set on off, it could also be used to step a separate reed relay or hall sensor uni-polar, bi-polar or bi-polar latch, Honeywell SS400 series, min LED's to set time on.
How do you intend an indicator of time set?
Max.
Hello Again

I think I am going to amend my initial post. I wish to have a control circuit that I don`t have to program the I.C and as for run time, it will be fixed for 10 sec. run and can you show same circuit with 15 sec. run time?
George
 

LesJones

Joined Jan 8, 2017
2,687
Does the 10 second timer have to start both when power is applied to the circuit AND when the reed switch contacts are open ? If so how should it behave if power is applied with the reed switch contacts in the open state ?

Les.
 

Bernard

Joined Aug 7, 2008
5,618
This works on a solderless breadboard after substituting a logic level FET for a transistor which was bad. Motor 3V @ 100 mA, so added R5 to bring load up to 600 mA.
Timing is by R1 & C1. T = 1.1 X R( meg ohm ) X C ( micro F ). C1 is marked as 10 uF but measures about 9.5 uF., so for 10 s R1 = .96 M & for 15 s =1.43 M.
To insure that 555 comes on reset @ power-up, pin 4 is held at ground for a split second by C2 & R3. Passing a magnet close to SW triggers 555 .
Use a pot. for R1 to set timing, then sub. with fixed R.Motor Timer 00000.jpg
 
Top