VK5TM


News, Updates and Other Minutiae

I have, for quite a while, provided modified versions of the code for my projects free of charge. However, the cost of webhosting for this site has tripled in the last couple of years and the little I make out of the pcbs I sell goes nowhere near covering this cost.

As of October 2017, I will be asking for a donation in exchange for providing custom modified code for my projects to help keep this site available.

As a lot of people have pics of things unrelated to ham radio on their websites, I thought I would add a couple of my own (Scroll down for site updates). Banjo, our Red Heeler/Koolie cross at 4 months old. Banjo at 4 months And at 12 months old (Feb 2016) enjoying his birthday breakfast treat of banana on toast. Banjo at 4 months A new addition to the family, an 11 week old kitten (end July 2017), rescued by Banjo after being trapped between a water tank and fence. Her name is Storm after her colouring and it's eating a bit of toast and jam (yes, our animals do eat strange things, including lemon meringue pie). They are now the best of friends. Storm at 10 weeks

October 2017

Simple DDS VFO project updated and software file uploaded. The pushbutton on the encoder is used to change step size (step sizes 10Hz, 1kHz and 10kHz).

September 2017

Noise Canceller kits now available.

July 2017

Updated both the DDS Xtal Substitute and DDS Xtal Substitute Mark 2 projects into one project. The original webpages are available to download as PDF's.

May 2017

New project added - my version of the X-Phase noise canceller. PCB available and a kit of parts to follow soon

27 December 2016

Another addition to the Gallery section. This time, fitting a DDS module to a Philips PM5326 RF Generator to cure a bad drift problem.

Encoder Headaches

Or - a trap most have fallen into?

While working on another custom modification of the DDS Module, I spent about a week banging my head against the wall, cussing, using other nasty words and throwing things around the workshop. Why? Because the !#%$* encoder wouldn't work properly when the DDS code was modified and migrated to an 8 pin PIC. Nothing to do with the encoder changed in the code transplant other than the pins it was connected to. Even looking at an oscilloscope wasn't helping (it showed the problem, but wasn't helping). Instead of getting this: encoder quadrateur phase I was getting this: faulty encoder quadrateur phase What on earth was going on? It was a brand new (if cheap) mechanical encoder. Tried changing pullup resistors and the value of the filtering caps (<- CLUE ) but nothing made any diference. Even went so far as to try Schmitt inverters and 'D' Flip Flops to try and cure the problem. Here is the snippet of the schematic as it relates to the encoder and I can tell you, the problem is right there, staring you in the face. encoder circuit Have you worked it out yet? Come on, it's simple when you know - keep trying. And no cheating by scrolling down. Annoying aren't I! Oh, all right, here's another clue - how are the caps supposed to discharge? Via the encoder when it's contacts connect to gnd I hear you say? Maybe so, but it's already too late by then. Besides, what are the caps supposed to do? Eliminate contact bounce, right? All right, stop yelling, here's the answer: Question, how can the caps eliminate contact bounce when they (the caps) are already fully charged and the software is configured as 'active low'? With 100n caps, the bounce time of the contacts is too fast to properly discharge the caps and the input pins of the PIC are high enough in resistance that they aren't going to help either, so nowhere for the spikes of contact bounce to go. Solution: modified encoder circuit This way, the caps are held discharged so that when the encoder contacts connect to ground, they are more easily able to absorb the small voltage fluctuations. With the values shown, I now get nice clean quadrature signals (don't be tempted to increase the value significantly, the trailing edge will develop a nasty curved appearance that will cause problems). Get out your scopes and cheapy mechanical encoders and try it. I know it solved my problem. (I had a couple of narky emails saying what a load of bull, but you can bet they didn't actually try it. Also, a couple of experimenters have reduced the caps to 1n and commented that it worked out better for them.)