Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

timer circuit needed

Not open for further replies.


New Member
I am looking for a timer circuit which will allow a series of off/on/off cycles. I am having trouble finding a circuit which allows variable duty cycles between resets. Here is a description of what the cycle must do: trigger signal, then off(delay) 16, on 1, off 8, on 1 off 8, on 1, off 8, on 1, off 16 on 2. These times are in seconds and are not exact but very close. The trigger signal will remain active through the entire cycle and then be removed to repeat the process. This circuit will be used to control the string tying motor on a round hay baler. Currently, the motor is manually stopped at the necessary positions by a simple on/off switch. The timer circuit will need to control a relay to pass the 12v to the motor that is derrived from the tractor battery. The baler has an indicator arm to show the diameter of the bale inside. This is where I will mount the trigger signal switch to activate the timer when the bale is the appropriate diameter to be tied. This switch will be released after the bale is tied and dumped out of the baler, as the indicator will return to the empty position, thereby releasing the trigger switch. It will reactivate once a new bale reaches the appropriate size. This process could be repeated up to 150 times per day, depending on the amount of hay in the field.
The easiest possible way is to do it using a microcontroller like PIC or whichever you like.
Have you considered a knob with some pre-set times to choose
before the next cycle is activated ?

I'm not quite sure what you want to do ...
The cycle must be completed in the order I gave in the original post and I would like to automate the whole process. The low intervals are when the haystring is wrapping around the bale. The "on" or high intervals will need to activate a relay to pass 12v to a motor on the baler which has a drive screw and stops the haystring at the appropriate places on the bale of hay inside the baler. Thanks for the responces.
Can You draw me a timing diagram for better understand? When i can completely understand what You need, i draw a circuit.
Here is the timing diagram. The times are in seconds and are very close but may need to have the ability to be adjusted to make the motor stop at the exact points. The trigger signal will be present throughout the entire cycle and be removed shortly after the 4 sec on. Thanks for the help. Please let me know if you need more info.


16 sec off

Does this cycle have to repeat when user decides,
Does it just keep cycling till it's told to stop ?

John :)
A trigger switch on the baler will activate the timer. This switch will be activated when the bale of hay inside the baler reaches the appropriate size and causes the triggerswitch to make contact. After the timer has performed its function of controlling the motor on the baler that applies the haystring, the bale will then be removed from the baler and the baler will be empty and ready to form another bale. When the baler is emptied it will break the contact to the timer from the trigger switch. At this time, the timer will need to reset to be ready to complete the timing process again once another bale reaches the appropriate size. Thanks for all the interest in my project.
Im not exactly sure what your setup requires since ive never seen a hay baler before, so i drew up this block diagram of a circuit that might work.

Would this be accurate ?

**broken link removed**
The block diagram looks right on track. I know it is hard to figure out exactly what I am doing without seeing the baler's operation. The main thing is that the timing sequence can be set in the pattern of:

1.Start of timing cycle begins with a 16-20 second pause. (I know the pause seems strange but during the pause or off position the motor is stopped as haystring wraps around the bale as it spins inside the hayroller.
2. 1 second on(moves motor to next position)
3. 8 second off string wraps around bale again
4. 1 sec on
5. 8 sec off
6. 1 sec on
7. 8 sec off
8. 1 sec on
9. 16 sec off
10. 4-5 sec on(this final motor movement brings the string over to a set of knives which cut the string. The roll of hay is now ready to exit the baler. The back of the baler opens via hydraulic cylinders and falls out of the hay roller. The back of the roller closes and the process of making another roll of hay is ready to begin again.)

If I need to give more detail on the complete operation of the hayroller please let me know. I think this will make a very interesting project and it will be quite useful for my hay production.
I want to add this about the timing cycle. Even though the times within the cycle are not the same, the complete cycle always has the same pattern.
If You need independent adjustment, i recommend a sequential timer with NE558 (quad 555).
How do I obtain the 16 and 8 second pauses between outputs? All must go to one relay which will pass 12volts to the motor.
I have seen 555 circuits which have a delay and then high, however, they remain high. Is there a way to set the delay time and high time? I might could use a series of 1 shots with each one triggering the next and tie them all in to the one relay.
Heh, strange you should mention it, i was just thinking the same thing.

Ive re-drawn the block diagram to include the NE558's that Sebi suggested earlier. These act as one-shots that are triggered in sequence by the 74154, the last output is used to reset the 7493 counter so the sequence repeats.
It would take abit of tweaking with the timing resistors to get it just right but i think it would work.

**broken link removed**
Oops i made a slight booboo, that should be 2 spares, i think your sequence requires 10 steps not 11.

Also after looking it over again ive noticed another problem. The circuit needs a means of stopping the sequence temporarily while a timer is busy generating a pulse. I think a gating circuit would solve that problem, anyone else see another solution?
Does the 74154 execute the trigger signals at the appropriate times? I think I have used one before in a basic led counter circuit.
Does the 74154 execute the trigger signals at the appropriate times?

No , not in this latest diagram. In the original block diagram the delay between trigger pulses was accomplished by taking different taps off the 74154, but after i realized your sequence required 10 steps, there wouldnt be enough timing taps on the 74154 to do that many steps.

I toyed with the idea of using two 74154's which would give us a total of 32 seconds to work with , but i dont think that would be enough either.

Another idea is to stringe a series of timers together with one triggering the next in a continuos sequence.

And if you are comfortable with programming, you could look into using a microcontroller, which was mentioned by someone earlier.
The total time from initial trigger to the last will be aprox. 60 seconds. I am not familiar with the PICs but am willing to try what ever setup will be the most feasable.
Not open for further replies.

New Articles From Microcontroller Tips