I’m still waiting for that replacement LCD to arrive from china, i’ve ordered another from a UK seller.
I’ve not been sitting around twiddling my thumbs though; a while ago i saw a schematic for a stepper motor driver on instructables. It seemed a little over complicated to me and i figured i could easily build one using one of the PIC microcontrollers that i have, so i set about designing a cheap 3 channel stepper driver using just a 40 pin PIC and some mosfets. The advantage here is that i can give it a number of interface options such as a parallel interface, an RS232 interface or an I²C interface. There may also be options to include an LCD for status display.
The stepper driver circuit had reminded me of another one of my projects and i got the itch to start it. This is my CNC project. Its an MDF construction and the plan is that it will eventually be able to build a better version of itself. I’ve already started construction so I should soon be posting my designs.
Ok, I’ve finally found time to make a new post about my Sunrise Word Clock. My previous attempt at making the circuit work on breadboard didn’t go so well. I assume this is because of the poor connections that the breadboard provides and could also have been because of poor layout choices. Anyway, I’ve rebuilt my prototype on strip board and i’m going to try and explain the circuit here.
The microcontrollers that i have readily available are PIC16F887. These come in a 40 pin DIP package
The interfaces i require are:
- 2 I2C pins
- 2 Vdd pins
- 2 Vss pins
- 3 programming pins
- 1 pin for analogue to digital
- 4 pins for button inputs
- 6 pins for LCD interface
- 22 pins for the Front LEDs
- 1 PWM Power LED Channel
- 2 Crystal Pins
Total pins required = 45… oh dear
My next update is taking a little longer than i had hoped. I have been building my prototype circuit on breadboard but it was behaving rather strangely. I would load my test program, all works fine then suddenly it would stop working. After unplugging things and plugging them back in again things would work again but then the next day the whole thing wouldn’t work. I finally got fed up with trying to get the breadboard circuit to work and i’ve been building my circuit on strip board (veroboard). This is a step that i was going to take eventually anyway but ideally not this soon.
The circuit is based around two pic16f887 microcontrollers. One is going to control the main clock functions and the other is going to control the lights on the front of the word clock.
Building this circuit on strip board is taking quite a while so please have patience, I hope to have a post up mid week describing the circuit.
- My Adjustable Voltage Circuit
- My Panel Meter Circuit
- My Aluminium Supply Case (Labelled)
- 2x DPDT switch
- Green Binding Post
- 4x Red Binding Post
- 4x Black Binding Post
- 3mm Red LED
- 6x 3mm Green LED
- 7x 3mm LED panel clips
- 4P2T rotary switch
- Amp Panel Meter
- Voltage Panel Meter
- Red Multimeter Lead
- 2x 6mm knobs
- ~20cm of 3mm 3:1 Heatshrink
- 2x TO-220 heasinks
- ~50 Crimp terminals
- Lead Free Solder
- 3x 47 KΩ resistors
- 3x 5.6 KΩ resistors
- 3.9 KΩ resistor
- 820 Ω resistor
- 12 KΩ resistor
- 1.8 KΩ resistor
- Soldering Iron
- Crimping tool
- Snipe nosed pliers
- Wire cutters
- Glue Gun
- Phillips screwdriver
- 2mm Allen key
For most of this it should be clear how it goes together. The circuit construction just followed my power supply schematic. If there is anything that needs explaining further then feel free to ask. Unfortunately i got a bit carried away at some parts and forgot to take photos, I’m still learning to take my time.
You may have noticed that my previous post shows strange labels for the rotary switch. This is because i’ve changed the function of the rotary switch.
The ammeter causes a small voltage drop and so when the ammeter is being used as ground, the effective supply voltage is different to when the actual ground is being used. As such i’ve made the switch have the following options for the voltage measurement:
- Variable voltage to Ground (VG)
- Variable voltage to Ammeter (VA)
- External probe to Ground (EG)
- External probe to Ammeter (EA)
As such the previous schematic for the power supply needs updating. Below is the updated schematic:
I think this is a slightly more useful design as it allows me to compensate for the voltage drop across the ammeter. The only function i lose is the ability to measure the fixed outputs. But considering the external probe should be able to do this, i don’t really mind.
Note: There is an updated version of this schematic here
I’ve been unable to get to the tools lately to finish off the bench power supply case, so thought i would do an update for people looking to do a similar project.
I’ve drawn up the circuit schematic for the bench power supply. I’ve given colour coded labels for the cables coming from the ATX power supply (correct according to wikipedia at time of publication) and shown all the circuits that are needed, including all component values that I’ve so far decided on. The resistors attached to the LEDs will be chosen at later date, hence those have no values in this schematic.
I hope you find it useful
edit: I should add that i have some planned upgrades to this, such as relays to switch the binding post outputs based on the state of the power good line. This should protect any equipment from unstable voltages when the supply is first turned on. Also I would like to put resettable fuses in line with the outputs to prevent over loading any of the components. These are complications that can wait though. For now i just want to get the basics working.
Since its taken me a while to get the next stage of my bench power supply project finished, I decided it might be an idea to post another electronics guide. I’ve added a brief article to the electronics guide section on basic tools used for electronics. It will be expanded on later to include other useful tools as well as more advanced tools
I’ve tried to include links where further information can be found and where some of the tools can be bought in the UK, alongside a brief description. I’ll slowly expand these links and hopefully you will find it useful.