Intro: Magic POV Wand (yet Another POV Toy)
NEW! (11/14/2014) This kit has been upgraded to a professionally manufactured circuit board and the price has been reduced to only $9 per kit. (And for educators, a discount price of only $8.00 per kit.)
This Persistence of Vision (POV) toy is simple to assemble and fascinating to play with. It is a good introduction to digital electronics and soldering. It works by flashing each column of “pixels” in rapid succession producing the illusion of text in mid-air. You can program in your own messages using two push-buttons. The message is saved in “Flash” memory and will remain in the MCU’s (PIC16F628a) memory even when powered off. The message can be changed as often as you like.
This POV toy is similar to the MiniPOV3 with a few important exceptions:
* Button cell battery - more portable. Easier to mount onto a bicycle or other spinning object.
* Change the message without using a computer.
* Less components to solder in.
* Less expensive ( Now only $9! )
Buy kits at http://www.chinchillakits.com/product/magic-pov-wa...
Step 1: What You Need
Everything pictured here is included in the kit. If you already have most of these components, you can order the circuit board and/or the programmed chip individually.
ID Qty Part
A 2 Momentary Push-buttons
B 7 Diffuse Red LEDs
C 7 200 ohm resistors
D 1 Mini Slide Switch
E 1 18-pin IC Socket
F 1 Programmed Integrated Circuit
G 1 CR2032 Button Cell Battery
H 1 Button Cell Battery Clip
I 1 Engraved Circuit Board
Step 2: Assembly
1. Begin by inserting and soldering all seven 200 ohm resistors. Make a nice tight 90 degree bend on both wire leads and insert all the way so that the resistors rest snugly against the board. Doing this will make it easier to install the LEDs between the resistors.
2. Install and solder in the slide switch and two button switches as shown in the diagram.
3. Now install the IC socket. Do not insert the programmed microchip yet. Solder it in.
4. Install the battery clip. (Notice, when installed properly the positive post extension will extend toward the center as shown and the battery clip itself will extend slightly past the end of the board.)
5. Finally install the 7 LEDs being careful to orient correctly. Notice that the positive leg (longer lead) will always be on the right when the board is oriented as shown.
Step 3: Testing the Circuit
Before installing the 18-pin pre-programmed microcontroller, you will want to test the circuit by following these steps.
1. Put in the battery (positive side up) and turn on the circuit with the switch.
2. Using a spare piece of wire stripped at both ends, insert one end into the IC socket pin 5. With the other end briefly touch the following pins to verify that the corresponding LED lights up. Note, only one LED should light at a time. Touch these pins in order to light the LEDs starting with the last LED on the right. Pin 9, 16, 15, 13, 12, 11, and 10. If any LEDs do not light up, carefully check the solder joints for short circuits. Use a hobby knife to ensure no solder is bridging from one track to an adjacent track.
3. If you have a digital multi-meter, it is also a good idea to check the operation of the push buttons. Resistance between pin 5 and 7 should go to zero when the right button is pressed and resistance between pin 5 and 8 should go to zero when the left button is pressed.
4. If all these tests pass, you are ready to turn off the circuit and plug in the microcontroller IC. Be sure to insert it the right direction. Pin 1 is indicated by a small indention on the IC, pin 1 should be inserted away from the LEDs. (Nearer to the battery)
5. Now switch the circuit back on. All 7 LEDs should be flickering. Take the circuit into a dark room and wave it in front of a mirror. If you see the letters ‘ABC’ repeated over and over again, congratulations, it worked! Now let’s move on and make your own message! See next page for instructions programming your own message.
Step 4: Programming Your Own Message
Changing the displayed message is easy once you know the trick. A message of up to 60 characters can be programmed, however long messages can be difficult to read.
Start by putting the circuit in programming mode. This is done by holding down one of the buttons (either one) while turning on the switch. The LEDs will briefly flash in sequence -Night Rider style- letting you know that it is ready to be programmed.
After you let go of the button, the microcontroller will display the pattern for the first character. If this is the first time you’re programming the message, you will see the pattern for the capital “A” which is that all LEDs are off except the one on the end. (see chart above) To change the first letter, press the ‘Change’ button (the one nearest the LEDs) repeatedly until the pattern for the desired letter appears. You may find it easier to say the alphabet to yourself as you push the button since each pattern will appear in alphabetical order. If the letter you want is in a different column of the chart, you will find it faster to press and hold the button. Holding down the button will fast-forward to the top of the next column and stop there. If you pass the desired letter, simply continue pressing and holding the button until you loop back around to it again.
Once the pattern for the desired letter appears, press the “Accept” button or the button on the left one time. Doing so will save your character selection and begin displaying the character that is in the second position. You then repeat the process by pressing the right button repeatedly until the pattern for the desired letter appears and then pressing the ‘Accept’ button.
IMPORTANT! After accepting the last letter of your message, you must accept one more pattern with all of the LEDs OFF ( pattern). This is the end-of-message indicator.
Finally turn the power switch off and then on again to try out the message. That’s all there is to it! Have fun!
Step 5: Ideas for Displaying the Message
Here is one idea for displaying your message. I'm sure you can think of some others.
Here I made a handle by turning block of wood on a lathe. You could accomplish the same thing by using a dowel. Get a 12" ruler or a paint stick and drill a small hole in the end. Insert a small screw through it into the end of your handle so that it can spin freely.
You can mount the circuit onto the other end of the ruler or paint stick however you wish. I simply wrapped a rubber band around it a few times.
With a little practice, you should be able to get it spinning smoothly with very little hand movement. For best results, take it into a dark room like a bathroom and spin it in front of a mirror. Keep in mind that if you are using a mirror, you will need to spin it in the opposite direction than if you are showing it off to people in front of you... otherwise the message will be backwards!