Author Archives: Pete

6502 Clock – A Blast from my past

This is not a PIC micro related post, nevertheless I think it is interesting.

This was a clock I built around 1985/86 using a 6502 microprocessor. It was the precursor to the ‘Record Time Clocks‘ I went on to build using an Intel 8748 microcontroller and eventually the PIC microcontroller based ‘Record Clock Redux‘ project.

The code was written in machine code – I didn’t have an assembler so I wrote the code by hand on paper – entered the HEX opcodes and used a disassembler to check branches and jumps went were I intended. I could work out relative branch offsets in my head at the time. I also knew most of the opcode HEX values from the top of my head. To this day I know that $4C is JMP absolute, $A9 is LDA immediate, $EA is NOP.

It still works, so the EPROM has not given up its data in 36 years. The EPROM programmer was something I built myself and again wrote the code to control it.

Back when this was built sourcing parts and components involved a printed paper catalogue, a hand written order form posted to the supplier, or by 1986 perhaps a phone call followed by a wait for the order to be delivered, and generally no next-day shipping either. Also I was young and didn’t have a lot of money so parts tended to get robbed from one project to build the next.

Record Clock Redux – Finally!

In May 2019 I started working on the Record Clock Redux project and I actually completed the code, milled out the acrylic backplate and genuine 7″ single record all ready to assemble into the final clock. However, things happened and it never got finished, in fact I have barely touched a soldering iron, or done anything PIC micro related since.

Anyway, I sat in the workshop in the middle of December 2021 and put the pieces on the workbench. I looked over them trying to recall how I’d intended it to fit together and I decided this was the time (pun intended) to finish “Record Clock Redux“.

Final Assembly

First problem I ran into was not having any PIC16F18325 microcontrollers in SOIC package. I checked my previous sources and no-stock until March/April 2022 so not a good start. At this point I could see how this might turn into another two years. Determined that I wasn’t leaving the workshop until it was finished I took a previous prototype PCB I had lying around and de-soldered the PIC for reuse. The control PCB was duly assembled, PIC programmed, battery installed and an initial test showed all was good.

The acrylic backplate and the vinyl record had been milled out on my CNC3018 router two years previously along with the smoked acrylic ‘windows‘ for the LEDs. A little reaming and counter sinking of the holes for the PCB mounting screws was all that was left to do here.

Next was the installation of the WS2812 RGB LED modules. I previously bought a large array of these pre-soldered onto small PCBs. I linked these together with Kynar wire then made up a short lead with 0.1″ Molex connector to the PCB. The LEDs and wiring were held in place using Kapton tape. I did this rather than gluing them in place to make it easier to fix any issues with the modules or wiring. As it turns out there weren’t any. The 7 segment display is a 0.37″ RobotDyn module using a TM1637 control IC.

To fix the 7″ single record to the acrylic backplate, I drilled a couple of 5mm holes in the backplate then positioned and aligned the record over the front and clamped it in place. The record is spaced off the back plate about 1mm, this allowed me to inject hot-melt glue through the 5mm holes which then stuck them together. It’s still possible to separate them if needed by sliding a knife inbetween the backplate and record; I know, I have done it 🙂

In retrospect I wish I had used some WS2812 LEDs in a 5mm round opaque package. This would have been true to the original and I hope diffuse the light better than the 5050 SMD parts. In fact I have aquired some and may yet build a redux V2 clock – maybe 😉

Original and Redux

It’s now 36 years since I made the original 12″ version of the clock. Ever since I started messing around with PIC microcontrollers it has been something I have always had in the back of my mind as a project I should do again. I’d kind of expected the original clock to die at some point and then I’d have a reason to do it, but amazingly its run 24/7 since 1986. Apart from a repair due to overzealous dusting breaking a wire to an LED, it just keeps going. It would be interesting to see if the PIC version lasts as long, not that I’ll be around to see that – 😨

So the photo below shows the original and redux clocks together for comparison. The original only displays the minutes on the 7-segment LEDs, while the new version using the 4-digit display shows hours and minutes, or minutes and seconds as well as the option to display temperature. One thing the original does better is the dimming of the display. The TM1637 has brightness control but it is in discrete steps, so the new verison has three stepped levels of brightness while the original does a pleasing PWM fade.

Navigation Lights for Models Update 2021

Recently I needed to revist the code for a project I did back in 2012 Navigation Lights for Models. In doing so I discovered that the latest version of MPLAB X (5.45) has dropped the old MPASM assembler and the version of assembler now being used doesn’t play well with source code written for the old MPASM assembler. I still have MPLAB X IDE V5.30 installed with support for MPASM and this works fine.

The reason I revisited this project was because over the years many people have contacted me having trouble getting it to work. A common cause is the calibration word in the PIC12F629 getting erased. Even I get caught out with it 🙁

Since the original code attempts to read the calibration word after power-on, if it’s not present the code just loops and the PIC appears to be dead. Since the timing is in no way critical for this application, I have reassembled the original code, skipping the bit that attempts to read the calibration word and instead writing a default 0x7F into the OSCCAL register of the 12F629/675. This way, it doesn’t matter if the calibration word gets erased or overwritten, the program will still happily run.

You can download the programmer ready HEX file for this new version below.

In the screenshot below, the calibration data is invalid, but we program the new code ignoring the warning and it runs just fine.

8 years after the original project was published, I was still able to find the demo board to verify the modified code runs correctly.

Compact Clock using TM1637 LED Module

In all the time I’ve been been messing around with PIC microcontrollers I’ve never done a simple 7-Segment LED clock, and it’s something I’ve always wanted to do.

For the Record Time Redux project I’m currently working on I needed to design a control board for it. I started working on a PCB layout and then thought, why not make the board so it could also fit on the back of the 7-Segment LED module. So I came up with the board shown here, it fits to the back of the 0.56″ RobotDyn 4-digit clock module (see here) and turns it into a compact USB powered LED clock.

I fitted the assembled boards into a Hammond translucent red 1591 style case (size 100 x 50 x 21mm )

Schematic and PCB layout can be found on the EasyEDA website here.

The source code is fully working, just need to get some time to write up a quick projects page and I’ll make it available then.

Update: 13/06/2019 – Full project now published here

Using Core Independant Peripherals as a 555 timer IC

There is an often used phrase “You should have used a 555” where a microcontroller has been used to do something a 555 timer could have done. So this got me thinking, could you configure the PIC microcontrollers Core Independant Peripherals to behave like a 555 timer? Read on for the answer.

While this may seem pointless, and yes I know it is, it was just something that I kept thinking about so in the end I had to do it to satisfy my curiosity. Anyway it’s a practical exercise in using the Code Configurator tool in MPLABX.

Continue reading

Tachometer Clock Project

A few months ago I came across a post on the Hackaday website that showed a clock made using an instrument cluster for a motorbike. The clock featured in the article was based on an Arduino but I thought it would be interesting to do something similar using a PIC microcontroller. I had a look on eBay and found them being sold under the description of “Universal Motorcycle LCD Digital Speedometer Odometer Motorbike Tachometer Gauge”, or something similar and going for around £20.00

So I bought one and a few days later it arrived and the fun began…. Read all about it here

Revised PCB design for Race Start Controller project

A couple of weeks back I decided to re-vist the F1 Gantry Race Start Lights project that I originally did back in 2009.

The new PCB has an extra header to make connection to relay modules easier and uses a double-sided PCB. It is functionaly the same as the original and uses the same firmware which is now free to download.

You can find out more at the links below:

Tachometer Clock update

This is just a quick update to say I’ve been working on this steadily for the last few weeks. The PCB finally arrived earlier this week and I’ve got a board assembled and working.

This project is proving somewhat of a challenge. I’ve now bought two Universal LCD instrument clusters to test with and this is where things got interesting.

The second one I bought came without any instructions, I contacted the seller and they said sorry, we don’t have instructions for it. Now you might ask why did I need instructions for this one if I’d already got one? The answer is that while they look identical, the second unit is different, you enter setup mode in a different way, it configures differently although it has the same options and the 20 pin connector on the back of the unit is wired completely differently. The four connectors on the other end are wired the same but I’d bought some 20 pin connectors so I could make my own connector cable up. This second unit also seems to be more consistent at converting speed to minutes compared to the other one.

Anyway, I’m just working through what I hope are the last few little issues and a more detailed write up is coming…