simple timer switch help

[gus]

hi,

im looking to build a simple circuit that will run a DC motor for a period of time, wait for another period while an object is transferred to the device and then run the motor in the opposite direction for another period of time..

ive done a bit of research and it seems the best way to run the motor would be to use a H-bridge.. but i was wondering if anyone had any links to a simple timer circuit that would control the h-bridge? 1 output high for say 5 seconds, off for about 10 seconds and then another output high for 5 seconds..

another option i guess would be just a circuit that makes the motor run one way for about 5 seconds, and then a second circuit that is triggered by a pressure switch that activates when the object is transferred and makes the motor run in the opposite direction.. would that be easier to build than the h-bridge and timer switch with two outputs?

any ideas or input would be greatly appreciated!

cheers
gus

 

[normad]

hmm.. do i know you gus? refer to these two threads.. they are regarding the same problem

https://www.electro-tech-online.com/threads/timer-switch.104806/
https://www.electro-tech-online.com/threads/555-begginner-problems-and-ltspice-simulation.104897/

 

[mbarazeen]

either way would be easy, i feel the 1st will be cheaper. whats the H-bridge have you selected?
also you didnt tell whats after 5sec reverse run? will it stop for long? or any trigger or again will run forword imediately? or will there be a start button?

 

[Hero999]

What's this for?

Normally limit switches and sensors are used. A timer might now be a very good idea because if the supply voltage is higher the motors will run faster than when it's lower whilst the delay of a timer is fixed so you can't be sure the event you're timing will take exactly the same period of time to complete.

If this is an industrial setting a PLC are often used for this kind of thing because it can be expanded and easily reprogrammed if the process changes. It also has the advantage of not requiring any soldering or assembly experience.

 

[mart_1986]

im after a the same idea i using going to use a plug in timer put how can i make the motorgo forward at 12pm and reverse at 8pm im using to open and close curtains

 

[gus]

hi again, thanks for all the replies..

it's for a project we have to do for uni as part of a mechanical engineering degree, one device we have to make mechanical powered which drives an object to a point and transfers the object to a higher platform where a second device that is operated mechatronically that has to drive in a straight line from its start point to the meeting point, and then back to the start point again, and we're only allowed to touch either device once..

we are fine with building the mechanical device, but seeing as we havent learned much about electronics (analogue or digital) in this course, the mechatronic device is where we are having a bit of trouble..

i have done a bit of research and downloaded CEDAR logic simulator and made a 4 bit binary ripple counter out of d flip flops and i hope to build that and use a 555 timer with a variable resistor for the clock..

and then hopefully use that to run the h-bridge by having the original state of the bridge to the forward motor position, and once the counter has finished, having it switch to the motor-off position and then once the counter has run its course again have the bridge switch to motor-reverse for another count..

does this sound like its feasible at all? is there any other way that anyone can think of that might be a more elegant solution to the problem? would i be better off just using a 4017 decade counter to do the counting for me than a bunch of flip flops?

and if anyone can suggest a good simple h-bridge circuit that would be ace too..

thanks again for all your help..
cheers
gus

*edit*
probably better to use a 4 bit binary counter IC, than a 4017 decade counter?

 

[mbarazeen]

4017 can do the job, can you draw a timing diagram for a complete cycle and post it? rather than your explanation its easy to realise by a diagram.

by the way what i understand is...
you need to have a sensor to detect that the object has arraived to the start point. that will start the DC motor in forword.
then another sensor to detect the object when it reaches the meeting point & hold it for a while?? then the motor reverses.
when the object returns back to its start point, it remains stopped?

so how about the next cycle? your target is completed when it returns to the start point? or else?

 

[pasanlaksiri]

Seriously how about move on to a microcontroller. But if you wanna do it without a microcontroller, project will be really interesting and big but you will learn lot.

 

[Thunderchild]

Seriously how about move on to a microcontroller. But if you wanna do it without a micro project will be really interesting and you will learn a lot.

yea this makes a good and very simple pic project

 

[gus]

hi again, thanks for all your help

the reason i didnt go for a microcontroller is that i really wanted to keep costs down as much as possible.. also, i'm more interested in learning how to go about doing it this way than programming it using code..

just to clarify the objective:

device is placed at the starting zone

device is triggered by a single physical motion (flick a switch, whatever)

device drives forward (approx 2m)

device stops and waits while it receives payload

device drives back to start

device stops

and thats it.. pretty simple really, i need to decide whether to time the whole thing in timed stages, or time the drive and then start the drive back when the payload is transferred..

i used CEDAR logic simulator to design a simple circuit using a 4 bit binary counter, 3 D flip-flops and a bunch of AND gates (see attachment)

im planning to use a 74LS161 4-bit binary counter and a 4076 quad D flip-flop IC. If it isn't clear how the circuit works, basically each time the counter counts a cycle, it changes the state of the D-flip flops, and then i used logic gates to determine the action that is desired..

basically, it goes forward for 16 counts, stops for 32, and reverses for another 16 and then stops completely..

is this a good way of doing it? or have i overcomplicated the situation?

then i need to use the logic to actually trigger the h-bridge itself..

ive had a look on the internet, and one of simplest circuits i could find is this one (see attached) that i took from (The Using MOSFETS Website: H-bridge using P and N channel FETs).

would this be suitable for my purposes?

would mosfets IRF9540N and IRF1405 be good to use? also, i am not entirely sure about the difference between mosfets and just standard fets.. would it be ok to use a standard N and P FET in this circuit as opposed to the more costly mosfet?

sorry for having so many questions!!

once again, any help at all would be appreciated..

cheers
gus

 

[Thunderchild]

hi again, thanks for all your help

the reason i didnt go for a microcontroller is that i really wanted to keep costs down as much as possible.. also, i'm more interested in learning how to go about doing it this way than programming it using code..

if you are already equiped to program pic's then it is no more cost, infact you will probably find yourself saving a lot in parts you no longer need to buy

 

[pasanlaksiri]

Man I think you better use a microcontroller like PIC. I really low cost and ur project will make more perfect.

 

[gus]

i dont know anything about PICs and i dont have the equipment to program them.. so to buy a programmer and stuff would cost me more than the individual components..

i will see how i go, if i cant get anything working in the next week or so, i will look at getting a PIC..

cheers
gus

 

[mbarazeen]

what i understand is you feel its enough to control it by time, not using sensors, in real life sensors are the right options. any how i considered as you said to have 5sec forword then delay for 10sec and again 5sec reverse operation, see the attached one, i have shown only the controller part, the particular outputs can be wired to H-bridge to control.
i tried to simulate, but in digital mode it refused to do it with cap, without cap its not showing corect reset.

hope you will understand how it works.

Edit: U2A is an AND gate, mistakenly i put OR, but stil it works.

 

[Dvinchy]

I belive this scheme is the best solution to your needs. The time's period is regulatable by resistor R1. Periods of turning (of on) are interrelated each other.

 

[Hero999]

Those capacitors would have to be huge do drive the motor at a low enough frequency to be usable.

It's also a good idea to stop a motor before reversing it, otherwise it may overheat and will certainly overheat if it's left oscillating for too long.

 

[Dvinchy]

Although the full bridge is much better than capacitors above.

 

[mbarazeen]

Dvinchy

this particular IC is for different application, not to make timing for motors. this is for high frequency switching and as Hero999 told, it needs a very large capacitor,the OP need a delay for load for the object. hope you didnt understand his requirement. i have slightly improve the schematic i have pasted before, also there is a flaxibility to use dip switches to set the required time delay by some more additional parts.

 

[Hero999]

Although the full bridge is much better than capacitors above.

That's better, with the full bridge you get the full supply voltage, with the half bridge the supply voltage was divided by half.

As mentioned above, this isn't the right way of doing it: the motor will smoke if it's reversed too frequently without being stopped first.

Reversing a motor when it's at full speed will produce nearly double the stall current at the point of being reversed, causing currents as high as a couple of hundred Amps, even for a modest sized motor. If the motor doesn't blow, then the semiconductors certainly will.

 

[mbarazeen]

see the attached with some changes, i simulated and its workign fine, dip switches can be added at the stage of 5 sec and 10 sec timer so that time can be set upto 32 sec for both.
hope it will full fill his requirement without a PIC, and using available ICs at local market.

Edit: use binary counter 4520 or any other (4518 only counts upto10)