Sunday 18 March 2012

MICROCHIP disappointments

I have spent the last seven days frustrated by failures of MICROCHIP PIC devices.

I don't mean "failures" in the sense of heat and smoke. I don't mean "failures" in the sense of faulty logical operation (we didn't get that far). I mean "failures" in the sense of not doing what the manufacturer says it can do.

Before we start complaining, let's be clear - I am a fan of PICs. I have been using them since the 90s. As readers of this blog will know, I've used them in lots of radio-related projects (such as the multi-mode beacon) and more recently in the virtual organ. I've also used them "at work" and in real-world projects, most recently the MTCLogic controller. I am a fan and - perhaps - being a fan makes it all the more disappointing when things go bad...

It started with a 16F628A. I had found some old code on the 'net and, since it was written for the 628A, I thought I'd run it in that device. So I got a sample, only to be frustrated by it.

I found that I was completely unable to program the device using either my ICD2 or my PICKit2. [Incidentally, the claim that PICKit2 DOES support the 16F628A is made here (where it does remind users that debug is impossible without an additional component)]. Most of the time, I got a failure on verification at a very low address, suggesting that no programming had happened at all. Occasionally, a few locations verified before failure. Once (
in an afternoon trying to debug the issue) I got a successful programming.

Not good enough!

I could program the device in my PICStart Plus - but I have grown used to in-circuit serial programming and wanted to use it here. Besides, MICROCHIP and all their documentation and code (I'm using MPLAB 8.7) CLAIM that this is possible.

A quick look on the internet persuaded me that I'm not the only person who has fallen foul of this discrepancy between marketing claim and experienced engineering reality, so I gave up and ordered a more modern 18-pin device - the 16F88.

On delivery I found that the 16F88 was up for being programmed with either ICD2 or PICKit2. Great! Until I tried something else which is CLAIMED to be possible - using debug mode on the 16F88 with the PICKit2...

Once again, this doesn't work - most frequently in the following failure mode...

(occasionally I could get past that point, but the subsequent debug operation did not work). I looked on the 'net and - you guessed it - this is a known problem.

I didn't want to have to change device again, so I tried debugging with the ICD2. That works.

I don't mind failure per se. I do mind when somebody claims that it is possible to... when it simply is NOT possible to. I don't care if it once worked for somebody. All I care is that it did not work for me and has wasted my valuable time.

Time which is far too valuable to waste posing questions like "why change the name of timer 0's interrupt enable flag from the simple "T0IF" (12F675) to the wasteful, redundant "TMR0IF" (16F88)". I suppose I should be happy and contented by the fact that the 16F88 does manage to do (most of) what is claimed for it.

...-.- de m0xpd

Sunday 11 March 2012

Volte-Face on Toner Transfer

Politicians do it all the time - so why shouldn't I? I've made a u-turn. A 180. A policy reversal.

I guess it really started this week, when I was trying to make up a little PCB for work - only about an inch square with a few SMT components on it...

However, it seemed to lie at the extreme edge of the abilities of my "Toner transfer" backyard PCB manufacturing technology (
blogs passim). It took me a couple of tries to produce a satisfactory batch of boards and I just don't have that much time to waste!

Fortunately, a mention on the G-QRP Yahoo Group this week had drawn my attention to a website, enticingly called "Blondihacks", produced by a talented engineer who rejoices in the name "Quinn Dunki". The particular link was to Quinn's description of PCB production, in which she summarises her methods for producing PCBs using pre-coated photosensitive boards. Quinn's descriptions and the frustrations of my week persuaded me to give it a try - so I ordered some board and developer from Rapid (who - once again - lived up to their name).

OK - here we go... Deep intake of breath... I hereby renounce Toner Transfer methods of PCB production. They may be cheap, but they are rubbish, compared to what can easily be achieved using photo methods. The quality of my first optical board comfortably exceeded anything I've ever made using toner transfer...

Don't waste your time with irons or laminators. Don't waste time trying to get rid of those irritating chalky deposits from glossy photo paper that get trapped between traces, that fill holes and that mess up fine detail. Don't waste time trying to use old magazines and suffer porosity in the etch resist and consequent discontinuities in the copper. Get yourself kitted out with some photographic technology. Do you detect a whiff of the zeal of the newly converted? That's me!

All I used for exposure was a UV-rich florescent tube intended for aquaria and an old picture frame. I'll work it all up into a "proper" light box eventually!

I didn't follow Quinn's advice about etching - my bubble-tank full of ferric chloride has never been a problem.

Incidentally, the PCB in question is a development environment for the MTCLogic controller - it replaces (by plugging into its DIL socket) the 12F657 PIC with a richer processor, with extra I/O and the luxury of a CCP module - just right for PWM applications...

As you see, there's MIDI input and output, an ICSP interface (here seen with an FCC68 adapter going to the ICD2, but equally at home plugged directly into my PICkit2), a couple extra analog inputs (by which system parameters can be adjusted using the prsets) and 4 digital inputs (to select options). As you gather, there are lots of exciting developments in hand on the Leslie controller front!

Incidentally, I like the way our American cousins say "a couple extra analog inputs...", as distinct from the English equivalent "a couple OF extra analog inputs...".

Do yourself a favour - get yourself down to Blondihacks for some well crafted, witty American writing surrounding some interesting and educational projects.

Do yourself another favour - ignore any previous advice seen on these pages advocating toner transfer.

Anyone want a knackered laminator?
...-.- de m0xpd