PIC Interrupter Program / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

PIC Interrupter Program

1 2 3 next

Move Thread

LAN_403

EDY19

Tue May 23 2006, 09:28PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

edit: Look down, objectives changed

Im looking for a 555 timer circuit that has a potentiometer to vary the frequency, as well as a potentiometer to vary the on time of the pulse, and I seem to be having trouble. Any ideas? (Its for a DRSSTC interrupter, but i thought it is more of a general question) Does anyone see an advantage to using a circuit tha controls the on and off time rather than the frequency and the on time? It seems the latter would be better, but maybe not

Avalanche

Tue May 23 2006, 09:44PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I've made a similar thing before by using a dual timer chip (7556)

The first timer has a fixed pulse width, of only a few microseconds, and has a pot to vary the frequency at which the pulse occurs. The output from this timer triggers the second timer (running as a monostable) which has a pot to vary the on time.

So in effect you have one pot for frequency, and the other for pulse width, or on time. It seems quite a precise way to do it, because there is no interference between the on time and the frequency when you adjust the pots.

Sulaiman

Wed May 24 2006, 01:03AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

A single 555 is adequate for ON time and OFF time of a typical(?) drsstc
In classic Astable mode the output is long ON time (high)
and short OFF time (low on pin3)
which is 'upside down'
"Single shot" is usefull.

EDY19

Wed May 24 2006, 01:20AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I was just thinking it would be nice to have it callibrated for bps from say 20 to 200 bps, and then on times from 0 to 200uS or so (not really sure, just guesses right now). With the other type (on and off time) the frequency would have to be calculated from the on and off times, id rather just look at a knob

Part Scavenger

Wed May 24 2006, 11:57AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Steve Ward's new interrupter does that IIRC... It's on his site, in the SSTC/DRSSTC section.

EDIT=> Yeah, right here

Quantum Singularity

Thu May 25 2006, 01:09AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

There are other chips available for freq and pulse width control... I dont beleive any circuit I have ever seen has 1 pot for freq and 1 pot for duty cycle on a 555. I could be wrong but I think in all the circuits I have seen adjusting 1 pot will throw off both parameters. Can anyone else corroborate this? I seem to remember building a freq generator from one once and having issues adjusting it to cover a wide range accurately with just one pot. Seems like you had to adjust both pots for a simple freq change to keep everything else the same.

EDY19

Thu May 25 2006, 01:22AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I'm actually thinking of starting a new project with this one- use a 556 timer to get the control with the on time and the frequency, then use a microcontroller to measure the frequency, and on and off times, and display that on an LCD screen (16x2). Any suggestions on how to start programming that? I'm going to look over the commands and see if i can figure something out, but any help would be greatly appreciated because anything i do right now is complete guesswork!

The TL494 allows you to change frequency with one potentiometer and duty cycle with the other, but in the layout i used, the duty cycle could only be brought from 0 to about 50%.

...

Thu May 25 2006, 02:27AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

um, if you are going to get a pic into the loop why not ditch the 555 altogether?

Any simple 14 pin pic should work fine, you use 7 lines for the hd44780 display, one for the output, and 2 for the pots... You don't need hardware anything on the pic, just create a r/c network across an i/o pin like

vdd-cap-pic i/o pin
        -pot-ground

then you set the i/o pin high, which discharges the cap, then you set it to input mode and wait until the cap charges through the pot below the threshold level of the pin(this time will be proportional to the resistance of the pot).

Since this is for a drsstc you can do the read the pots/display the value/calculate the required number of cycles for the on part and the rest of the off part during the 'off' part of the burst. Then you just wait the calculated amount of cycles, then turn a pin on for the required number of cycles, then read the pots/etc again.

rupidust

Thu May 25 2006, 02:52AM

Banned
Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85

If you go PIC route, you are moving into a Function Generator. And like ... said might as well get rid off 555 and external chips. The code to count and constantly update an LCD is more involved than that of the code to change duty and frequency, from an experience view point. If you have not done either, the difficulty is the same.

I have already done this for booster and ignition coil drivers with/without LCD. Whats the difference? The load and the feedback.

3 button booster interface.
1144021134 110 FT6457 Lcdbooster

Also see reference post:

Wolfram

Thu May 25 2006, 09:12PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

I started a project like this once, and BjÃ¸rn wrote some excellent routines for the timing. You gave them the number of ÂµS on-time and the number of ÂµS off-time and it generated the squarewave. I was going to use a button-triggered interrupt to set the freq/duty cycle. I was going to make three modes, freq/duty cycle, freq/on-time, and on-time/off-time. If it's okay with him, I'll post the routines here.

1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob