Persistence of vision or POV in short is commonly found in electronic projects and there are a multitude of kits that you can buy out there.
The electronics club in my college wanted to make a hands-on lab for the juniors and my lecturer chose the POV project. He bought a kit as a sample and I had to reverse engineer it so that we can make the kit ourselves and save a whole lot of money.
Here’s the kit from Nixie Electronics.
And it costs a whopping RM 240 (or USD 80) !
Why buy when we can make it ourselves 🙂 Let’s begin.
Using EAGLE, I draw out the schematics and also the PCB.
I designed the PCB to fit in a standard 25cm by 15cm board. I can make two sets of PCB using one board.
Printed out the PCB layout on a transparency sheet and the fun begins!
Exposing the UV board to fluorescent light for about 10 minutes. Used a heavy glass to press on the transparency sheet.
Because the board is quite big, I shifted the light source to the other side at around 5 minutes to ensure every part of the board gets an even exposure.
After exposure, the board is immersed in a sodium hydroxide solution to wash off the exposed photoresist layer.
Next, the board is immersed in a ferric chloride solution. Ferric chloride reacts with copper to form copper chloride. In other words, the copper on the board will dissolve in the ferric chloride solution but the photoresist layer that is covering all the tracks will protect the copper underneath from dissolving, thus resulting in copper tracks formed on the board.
Half way through the process. You can see the parts without the photoresist layer are being dissolved.
Do not dispose the ferric chloride solution by pouring it down the sink or drain! Find a proper chemical disposal service or at least just store it in a plastic bottle for the meantime.
The PCB in its’ full glory after the etching process is complete.
Got myself a pretty nice handsaw to cut the PCB.
Stanley MiniHack, can be found in most hardware shops for around RM 10.
Product link : http://goo.gl/7TU68
Almost perfect cut.
Drilling holes for components to go through.
To mount the DC motor, I had to go get some screws from a specialised nuts and bolts store. Couldn’t find it at a regular hardware shop.
Fitting the DC motor on the PCB. Thank god I got the measurements correctly when drawing the PCB. All the screw holes lined up perfectly.
The board with all the components on.
The spinning PCB. I used blue super-bright LEDs instead of regular ones.
Testing the PCB.
Now comes the hard part. The issue now is getting power to the spinning board. Because the board will constantly spin, you can’t just solder jumper wires.
We have to make use of the rotating spindle of the motor to transfer the power because it moves together with the spinning board.
Noticed that I carried a track to one of the screws on the motor? That is ground. The body of the dc motor is actually electrically connected to the spindle.
So that is half the work done, what about 5V?
We can create another layer on the spindle by first insulating part of it. I devised my own way that is to use shrink wraps. Bought the smallest diameter available.
Cut it to about half of the spindle’s height and apply heat (use lighter or match stick). It will shrink to the size of the spindle nicely.
Wind an exposed copper wire around the shrink wrap.
To transfer 5V to the outer part of the spindle, let’s turn to the PCB first. There are two big square pads beside the motor. They are connected to 5V.
Now we need to solder something to the pads that will make a connection to the outer part of the spindle. Take note that the spindle must be free to move.
I sacrificed a pen and took out its’ spring. Stretched it out and cut to the correct length.
The spring is actually made out of a wire that has elastic tension. We can make use of that to create a tension so that it is always in contact with the outer part of the spindle.
With that sorted out, we can proceed to mount the spinning board on the motor.
First, connect the ground to the inner part of the spindle. I used the wire connector (I wished I knew the proper name). See the picture below.
Took out the inner connector to use it to secure the ground wire to the spindle.
And the 5V connection to the outer part of the spindle. It will be quite a squeeze to get a soldering iron in between.
The last step is to drill holes for the mounting bracket. It is just a regular L bracket that can be found in all hardware shops.
Quite a tight fit, might need to change the PCB layout a bit in the next revision.
I haven’t figured out what to use for the base yet. Might need to use the mechanical lab to fabricate a heavy steel base for this. In the meantime, I just use a G clamp to secure it to a table.
Let it spin 😀
This project utilizes a PIC16F84A to blink the LEDs to form the characters.
The code can be downloaded below.
Thanks for reading.