Joe's Hobby Electronics
  • Joe's Hobby Electronics
    • Electronics Blog

Another clock... I love clocks...

15/10/2013

0 Comments

 
I've got a thing for clocks... I wonder if it's because I'm not getting any younger.
Anyway, I had a day free over the weekend and decided It was clock building time.
There's not much to this clock really. A PIC18F25K22 running some simple firmware written in AMICUS18 BASIC. There's a Dallas DS1302 RTC chip with battery backup, and a handful of other components.
I've been experimenting with different firmware to see which makes the display the most readable.
The image on the left of the clock front is showing a time of 10:20:13

UPDATE 29/10/13
I've created a construction project for this clock which can be found here.

0 Comments

Update to the PIC Digital Thermometer & Clock 

18/8/2013

0 Comments

 
When I'm not in the workshop, I usually switch off the clock; no point in wasting electricity.
The other day, when I turned the clock on, I noticed it was running a few minutes fast but once I reset the time, never gave it another thought.

Yesterday I switched the clock on and the time was completely incorrect. A quick check of the battery backup voltage revealed the problem; it was down to around 1.1v which is odd as it's a rechargeable cell and the recharging is supposed to be controlled by the Maxim DS1302 RTC chip.

I checked the firmware source code against the RTC datasheet and the error immediately became obvious. A bug in the code that's taken nearly two years to come to light, meant I wasn't specifying the charging options incorrectly. I've corrected the problem and updated the project files to include the fix.

This is an interesting reminder that even in the simplest of projects, some bugs can take a long time to surface.

0 Comments

Completed the Nixie Clock

13/5/2012

3 Comments

 
It’s been a busy couple of days playing with the Nixie Clock but it’s been well worth it.

The firmware for the PIC is completed and running and the main logic board that contains the PIC, RS232 interface, Audio Amplifier, HT and +5v PSU is complete and working.

I had to make a few “modifications” to the wooden case as the display board PCB was slightly too wide and the 7-way Molex connector was catching on the side, preventing the board from sliding into place. Thank heavens for electric files !!

The chap who will be receiving this is a bit of a change freak and loves things that are configurable, so every parameter can be configured by hooking the clock to a dumb RS232 terminal.

There is provision for two temperature sensors to be connected, and you can set alarms if minimum or maximum temperatures on either channel are exceeded. Alarms are either flashing coloured LED’s and/or an audio alert (frequency configurable of course).

There is provision for the CPU to power down the Nixie tubes during a specified time window. This could be useful during the day when the owner will be at work and should help extend the life of the tubes.

The on board RTC (DS1802) can have its date / time  set via a simple command over the serial port, and is also responsible for trickle-charging the on-board NiMH back up battery.

All that’s left to do is fit everything into the case and possibly make a few alterations to the firmware. I’m using just under 25% of the available program space, so theres lots of room available for additional features. I’ve also added an 8-way Molex connector to the top of the PCB that brings out +5v, 0v and the remaining unused I/O pins from the PIC; this will make hardware expansion simpler when it’s required; and it will be required at some point.
I've marked all the connectors so that when enquiring hands take the darn thing apart, it can be put back to gether... that's going to happen at some point as well I suspect.
Picture
Picture showing back wooden panel with interface connector, logic and driver board.
3 Comments

Nixie Clock - MK2

11/5/2012

0 Comments

 
Many years ago, I constructed a Nixie tube based clock for a friend, and whilst it worked, it never really worked well. It had an MSF decoder so could automatically synchronise itself from the radio clock at Rugby in the UK (since moved to a new location). However, with all his computers, PSU’s and other radio equipment, the MSF receiver never worked properly. Also, I never gave the design that much thought. It required a cumbersome power supply arrangement to drive the logic and provide the high voltage for the Nixie tubes. I used a PIC microprocessor to control everything but I ran out of program space so the project never reached its full potential. I also ran out of time and enthusiasm which didn’t help.

However, since I’m now officially on vacation for a week or so, I thought it would be an interesting project to re-do, and this time, do it properly.

This time I’ll approach the project in a slightly different way. Instead of one large PCB attempting to house everything, I’ve gone for a modular approach. This will make hardware upgrades a lot simpler in the future and allows the project to be constructed and tested in blocks which will cut down on re-work time if a fault is found in a specific area.

The picture below shows the major building blocks of the project.

At the rear is a small PCB that contains a simple high voltage (HV) inverter. This is really just a prototype and will be re-worked into a complete PSU board for the final build. It’s running from a 9v DC output from my bench PSU and producing the 150v DC to drive the Nixie tubes. The output voltage is adjustable via an on-board variable resistor.

The large board in the middle is the completed display board. This contains a 64-bit shift register constructed from eight 74HC595, 8-bit shift register ICs. There are also 50 x MPSA42 High Voltage driver transistors on the board to control the Nixie tube cathodes; all the tube Anodes are connected to a common HV rail via 47K resistors. There are also 9 x LED’s mounted in strategic locations at the front edge of the display board and these will be used to display operating mode; date, time, temperature, alarm trigger etc.

In the picture foreground you can see a small breadboard that is currently home to an 18F25K22 PIC  on a carrier PCB, and various connections to PIC programmers, and my Shift Register monitor device (described in previous blog entries).

The completed unit will contain a Maxim DS1302 Real-Time-Clock chip with battery backup, and a serial port interface for unit setup. There will be support for two temperature sensors (one internal, one external) and temperature / date/time alarms.

The possibilities are almost endless and I’m really only constrained by the amount of code I can squeeze into the PIC, which should be substantial as this PIC is a far cry from the previous one I used that had only 1K of program space.

The advantage of using the 74HC595 IC’s becomes apparent when you realise that you only need a total of five CPU I/O pins to control the shift register chain (and you can do it with less if you really want to). This leaves plenty of PIC I/O pins for other uses. Also, if an upgrade to the display board were ever required, the shift register chain can be lengthened without impacting on the rest of the hardware.

If you need to create a project that has a lot of inputs or outputs, the 74HC595 and 597 IC’s are perfect.
Picture
Nixie Clock running display test program.
0 Comments

Clocks... Clocks... Clocks...

9/1/2012

0 Comments

 
Now I love clocks, I really do. They are great projects because you can place them on the mantelpiece or in other prominent locations as a functional working device, partners can’t complain about it being another piece of junk because they do something useful, they come in all sorts of shapes and sizes and are great beginner projects and once you’ve built it, you can tell people “I made that”.

Recently, I’ve been working on a new clock project and it suddenly occurred to me that except for the physical display aspect of the clock, the internals are nearly always the same. A battery-backed RTC for the date/time (usually a Dallas DS1302) with support components, a PSU section of some type that usually puts out 5v for the logic and possible an additional higher voltage for larger LED displays, a PIC to glue everything together and some display driver hardware.

The only really custom part is the physical display, and the PIC firmware, and this got me thinking; “Can I construct a generic clock that can have many different displays connected, and just need to update the PIC firmware as required”?

So, this is what I’m currently working on. Some more thought is required on some of the projects finer attributes but I have an initial prototype sat on my breadboard that’s driving a strange looking LED display with 60 LEDs on it (I’ll post pictures later) and it seems to be working well.

The next part is to design several other display units and make sure that they can be driven by the hardware.
0 Comments

    Author

    A software and hardware engineer who loves retro computers.

    Archives

    March 2022
    September 2021
    April 2021
    June 2020
    May 2020
    April 2020
    March 2020
    September 2019
    January 2019
    April 2018
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    May 2015
    April 2015
    March 2015
    January 2015
    December 2014
    September 2014
    August 2014
    April 2014
    March 2014
    January 2014
    October 2013
    September 2013
    August 2013
    July 2013
    June 2013
    April 2013
    March 2013
    January 2013
    September 2012
    June 2012
    May 2012
    April 2012
    February 2012
    January 2012
    December 2011
    November 2011
    October 2011
    September 2011
    August 2011
    July 2011
    June 2011

    Categories

    All
    18f25k20
    18F25K22
    1-wire
    2114
    2764
    3D Printer
    3D Printing
    74hc595
    74ls595
    86-0325
    8MHz
    Access Speed
    Acorn
    Acorn System 1
    Alarm
    Aluminium Panel
    Amicus
    Amicus18
    Amicus Basic
    Amplifier
    Antex 1107
    Anti-static Mat
    Arduino
    Assembler
    Backlight
    Bargains
    Basic
    Bat
    Batdetector
    Bat Detector
    Bats
    Bench Audio Amplifier
    Bench Light
    Breadboard
    Bubbler
    Buck
    Bug
    "C"
    Cable
    Cable Gauge
    Cable Wire Size
    Capacitors
    Catalogue
    Clive Maxfield
    Clock
    Clocks
    CMOS
    Common Emitter
    Compiled
    Compiler
    Connector
    CPU
    CPU Simulator
    Crownhill
    Custom Computer
    Custom CPU
    Damage
    Develop
    Diode
    Diptrace
    Double-sided
    Double-Sided PCB
    Dry-joint
    Ds1302
    DS1820
    Ds18b20
    Ebay
    EEPROM
    Electronics And Circuits
    Eprom
    Erase
    Etch
    Evaporator
    Failed Capacitor
    Fake
    Fax Paper
    Ferric Chloride
    Fire Hazzard
    Firmware
    Florescent Tube
    Health And Safety
    Hidden Part Numbers
    High-Voltage
    Hv
    IC Test Clip
    IC Testing
    In Circuit IC Testing
    Incubator
    INS8154
    Instruction Set
    Inverter
    Kickstarter
    Laser Cutter
    Lcd
    LM2596
    LM386
    Logic Analyser
    M7MOJ
    Maxim
    Maximum Current Rating
    Mega
    Mit
    MITx 6.002
    MK4
    Molex
    Mosfet
    NE555
    Nixie
    Nixie Clock
    Npn
    OXO
    Oxo Machine
    Pcb
    Pic
    Pic Basic
    Pickit2
    Pickit3
    Pic Programmer
    Pixy
    Poster
    Pre-amp
    Prices
    Programming
    Project Box
    Project Case
    Project Enclosure
    Propagation Delay
    Psu
    Psu Failure
    Qfn
    RAM
    Rapid Electronics
    Raspberry Pi
    Regulated 5v Psu
    Regulator
    Repair
    Review
    SAD (Segment Address Decoder)
    SCC
    SCC MK4
    Seven Segment Display
    Shift Register
    Silient 700
    Slow Progress
    Smoke
    Smps
    Soldering
    Speed
    Speed Test
    Stepper Motor
    Supression
    Swg
    Switch Box
    Tank
    Tantalum Capacitor
    Temperature
    Temperature Sensor
    Texas Instruments
    Thermometer
    Tic Tac Toe
    Tic-tac-toe
    Timer
    Tools
    Traffic Lights
    Transistor
    TTL
    Usb
    Uv
    Vbe
    Vcb
    Vce
    W65C02
    Wash
    Weller
    Wirecutters
    Wire Cutters
    Wire Strippers
    Wiring
    Wp3eu
    X2 Capacitor
    X Capacitor
    Y Capacitor

    RSS Feed

© Joe Farr, 2011 - 2022 - Email: HobbyElectronics@kcsl.uk.com