- 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.
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.
The panel meters for my DIY bench top power supply have arrived from china. One is a 20v voltmeter and the other is a 5A ammeter. I ordered them from ebay and at a cost of around £6 each, they are far cheaper than anything available locally.
On unpacking the meters i found this rather interesting note:
It seems that the meters require fully isolated power supplies. It may be possible to power them from battery but then i have to mess about with relays switching them on and off and changing the batteries. Instead i hunted around and ordered some of these DC-DC modules. They are XP-Power IA1209S modules but any dc-dc module with between 9v and 12v isolated output will do. I chose these because they have a 12v input, 9v output and are cheap. They have dual outputs but this just means that they provide a -9v output as well as the 9v output. Obviously the -9v output isn’t needed.
Panel Meter Power Circuit
- 2 XP-Power IA1209S dc-dc modules
- Small piece of strip board (also called vero board)
- 6 lengths of multi-core wire (7/0.2mm core)
Only basic tools are required for this circuit. These should form part of any electronic engineers arsenal, as discussed here. I just used the breadboard as an extra step
When they arrived I tested them on breadboard first:
I’ve drawn up a nice schematic to show how simple the wiring is:
Remember to cut the tracks on the board between the two supply’s outputs if you’re using strip board.
This time I powered up the circuit using the jump starting trick i mentioned in my previous post and tested the output using a multimeter. The output read 10.5v but there was no load on them so this isn’t unusual. After wiring up one of the panel meters, the output voltage dropped to a more sensible 9.3v
Notice that i have a power resistor (large white block) to load the supply and ensure i get a nice consistent dc source. This is sitting between 5v and ground and is 10Ω. This gets quite hot so until i can give it a heatsink and some airflow, i’m only running the supply for short periods.
Next i soldered the dc-dc modules to some strip board in the layout shown in the schematic above. Remember to cut the tracks between all the outputs of the dc-dc modules, you want those outputs to be completely isolated.
The result is some nice blue:
You can see the circuit in the top right, just below the ATX cable connector. I used a salvaged piece of stripboard from my earlier mishap, hence the additional yellow wire to bridge previous cuts. The breadboard is just to help distribute power and to hold the power resistor.
My next step is making the aluminium box that all this will go into. After that it won’t be long until this project is complete
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