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
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.
Ok, so the components have arrived. No doubt I’ve forgotten something and will have to order some more.
I’m starting with building the variable voltage circuit.
- Micrel MIC29152WT low drop out adjustable voltage regulator
- TO-220 heat sink
- small piece of strip board (also called vero board)
- solid core wire
- 5kΩ potentiometer
- 560Ω resistor
- 10µF capacitor
- 22µF capacitor
- Soldering Iron
- 12v power supply
This schematic is taken straight from the voltage regulator data sheet. Vin is the 12v from the power supply, R1 is the potentiometer and R2 is the 560Ω resistor. The capacitor on the left is 10µF and the capacitor on the right is 22µF.
I calculated the resistor values using the equation in the schematic. These values should give a good linear range. If you have a different value potentiometer just try and keep the ratio roughly the same between it and the resistor.
If you don’t understand the electronic symbols then i strongly recommend you look them up. There are guides out there with pictures instead but you will soon get stuck when it comes to the more advanced circuits.
The pins on the voltage regulator have a 1.7mm spacing so to get them to fit in the strip board i simply bent them as shown here:
Since this is a very simple circuit, i didn’t bother drawing up a circuit layout. I just built it on strip board:
If you look closely in the circuit above, you can see i’ve inserted a small piece of plastic between the regulator and the resistor. This is because they are very close to each other and i was worried about them shorting out. I haven’t attached the heat sink yet, I didn’t need it for testing and i forgot to buy anything to fix it on with.
I tested this circuit by hooking it up to a bench supply at work and testing the output with a multimeter but if you don’t have access to a bench supply, you can power it straight from the atx power supply. Connect the +ve to a yellow 12v wire and the -ve to a black ground wire then short the green wire on the power supply to any black wire. If your supply doesn’t turn on, it may be that you need to draw more current from it. Try attaching a fan, power resistor or old cd drive and trying again. There are many instructions on doing this on the internet, just search for ‘jump start power supply’ on google or follow this link