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Interruptor / my first PIC project

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Sulaiman

Tue Mar 20 2007, 12:27PM

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

I have finally decided to join the modern world and I'm building an Interruptor for TC use with a PIC microcontroller.

(Technically it's my second project as I made a led flasher by copying circuit and hex code direct from the internet, without understanding the hex code. It worked so I feel a little more confident to proceed)

I sampled a PIC16LF84A (for the led flasher) and a PIC16F690 for this project
and bought one of those JDM programmers off eBay
I should have got an original PIC programmer from Microchip
the debug facilities would have been worth the extra
too late now - carry on regardless.

The current design is for a 20 char x 2 line lcd display with pushbuttons for;

Ton The on time for gating TC operation in DRSSTC mode etc. to be adjustable from 1 to 999 us
Toff The off time between ON times, 1 to 999 us
PPP Pulses per packet. From 1 to 999 ON/OFF pulses continuously
PRF Packet repetition frequency, how often a packet of pulses is produced, from 0 to 999 Hz

RUN Press and hold to produce output, release to modify variables

MCLR in case of latch-up etc.

So far I have done the (for me) easy part, the electronic board;
here are some photo's

The black connector is for 0V and +5V
The blue connectors are for 0V, RA2 the output, and RA0 and RA1 as yet un-assigned.
The yellow blocks are capacitors (100nF MKT) are part of the switch de-bounce,
since I don't fancy programming de-bounce software yet, and they make convenient locations for labels.

I shall make a second board for 230Vac to +5V regulated, a TC4421 output buffer, and an invertor for the EL backlight.

I haven't even worked out how to get to the assembler in the Microchip MPLAB IDE software yet,
so progress will slow down for a while !
Hopefully updates are to come

Any suggestions / comments welcome.

How many members have done something similar?

(i.e. who can I call for help ? )

ShawnLG

Tue Mar 20 2007, 04:14PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

I would put it in a shielded box to protect it from RF, also include RF protection for the input, outputs, and power port if possible.

Sulaiman

Tue Mar 20 2007, 04:22PM

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

I may do that, but initially I will be running the interruptor far from the TC by using a TC4421 to drive a long 50 Ohm co-axial cable, and maybe I will run the interruptor off a 12V VRLA Battery for good isolation.
This together with the need to continuously press the RUN button,
will hopefully keep me from getting too 'adventurous' near the running coil.
Two-person operation required for close proximity 'testing'

I've considered using fiber-optic coupling but can't be ar5ed.

If I do have problems after that I'll put it in a metal box.

I actually remembered to make allowance for mounting holes with this project!
I often end up with a board layout that results in double-sided-tape for mounting

Thanks for the reminder anyway.

Bjørn

Tue Mar 20 2007, 04:29PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

It looks great so far. None of your numbers fit in 8 bits, it would not be a challenge otherwise so that makes sense.

It looks like you have selected a 20 MHz crystal, that will make it possible to get 1 us accuracy without using all the tricks in the book.

I look forward to see the progress.

Wolfram

Tue Mar 20 2007, 05:09PM

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

I have been working a bit with something very similar, it was going to use a 2x16 LCD/VFD and some buttons and a rotary encoder for input. This was going to be for SSTC stuff exclusively, I was going to make a DRSSTC version later. On and off time was going to be adjustable between 0.0 and 999.9ms and it would calculate and show the frequency and duty cycle. I managed to finish all of the display handling code, and I had the main timing loop all figured out. It was going to run at 4MHz, 1ÂµS instruction cycles, the main loop was going to be 100 cycles long, and it would take care of reloading counters and checking buttons. As soon as it detected input, it would disable the output, modify the appropriate registers, show the new on/off time, duty cycle and frequency and then go back to the main loop with the new timing. Until I realized a normal 555-based interrupter would do just as fine, and that sparks from running halfwave rectified mains uninterrupted look much nicer anyways.

I'm still considering making one for DRSSTC duty, where close control of the interrupter timing actually matters.

If you need any help with display driving routines or things like that in PIC assembly, PM me.

BTW, I think 1-999ms would be more appropriate for Toff in DRSSTC duty.

Anders M.

Sulaiman

Tue Mar 20 2007, 07:32PM

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

I may not have clearly explained the proposed timings,
a little diagram;

This is shown for example with PPP = 4 pulses per packet

The idea being to set Ton (e.g. 200us) as large as possible without over-current in the output transistors
Then give a small break (e.g. Toff=100us)
Then have PPP number of these pulses in a 'packet' to grow the streamers (e.g. 4)
And finally to have PRF packets per second (e.g. PRF=100 packets per second)
If PRF=0 then there will be only one packet per press of the RUN button.

101111

Tue Mar 20 2007, 08:52PM

Registered Member #575 Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263

I have done something very similar just using a 555 timer, but I have always liked look of fancy LCDs so Iâ€™ve like to have the circuit schematic if you donâ€™t mind.

First post! :D

Marko

Tue Mar 20 2007, 11:43PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Well, great work..

I have one simple reason why I dislike metal shielding boxes: they give me shocks as I'm in proximity of the coil!

If I want shielding, I just use aluminium tape on inside of a palstic box and ground it.
And my current interrupter withstiff layout seems like it doesn't even need it.

Sulaiman

Wed Mar 21 2007, 07:52AM

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

Waco,
I certainly don't mind sharing the circuit diagram-
assuming I get the software working!

I wouldn't encourage you to follow my design yet as it's untried.

IF I get it working well I'll definately 'publish' the circuit diagram and the software.

Don't hold your breath though!

Steve Conner

Wed Mar 21 2007, 12:04PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Looks great, Sulaiman. I have made an interrupter with a PIC before (a PIC16F870 IIRC) but it was for a very specialised application. The Toff had to be pseudo-random, the Ton didn't matter, and the number of pulses per burst had to be adjustable by a trimpot.

So I just wrote code to cover this special case, and never got round to trying a general purpose interrupter algorithm like you're doing. My analog DRSSTC interrupter works fine for me, and it took me less time and effort to design and build than a digital one would have, but I'm happy to help any folks who want to make a digital one.

BTW, for isolation, I did in fact use a TC4422 driving a 50 ohm coax, which drove a pulse transformer at the Tesla coil end.

I used a bare board, but double-sided PTH. I found that the MCLR\ line had to be jumpered solidly to 5V, or the PIC would reset itself mid-burst from time to time. Even with the pull-up resistor, it still picked up enough EMI to reset.

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