Rolling Message Display Electronics Kit

By Ben Arder

Description: Rolling Message Display Kit
Experience level: Intermediate
Time required: 2 hours

Today I picked up my rolling message display kit. I thought to myself, what text will I have scroll from one side to the other? I had up to 16 characters to choose from. I ultimately came up with ‘I ♥ Jameco’ and I had a great time building it.

Building the Display Kit

1. I started by taking out all the components and organizing them both by type (resistors, capacitors, etc.) and value.

2. I set up all 5 of the jumper wires into their corresponding places on the circuit board and then soldered them into place.

3. I set up all 6 of the 330Ω (the Orange-Orange-Brown line resistors) resistors in spots R1-R6 and soldered them in. I then set up all three 0Ω (Black line only) resistors and soldered them into spots R7-R9. I then set up all four 2000Ω resistors in spots R10-R13 and soldered them.

4. Making sure the shaded line on the diode lined up with the shaded line on the circuit board, I set up and soldered the diodes into places D1-D5.

Set up the jumper wires
Soldered the diodes into places

5. I set up and soldered the 100nF (marked as 104) capacitor into spot C1. I then set up the 22pF capacitor into spot C2 and soldered it.

6. Paying close attention to the polarization of the electrolytic capacitors, I set them up in spots C3 and C4. I took special care to ensure the longer wire went in the "+" spot and the shorter wire into the "-" spot.

7. After the electrolytic capacitors were soldered in, I began to work on the LEDs. LEDs are polarized, so special care must be taken to make sure they are oriented correctly. They must be set up so that the cathode (the short wire) goes into the shaded hole, and the anode (the long wire) goes in the non-shaded hole. I set them up and soldered them by only soldering a few LEDs at a time. Eventually, they were in spots LD1-LD36. This way, I wouldn't accidentally connect two LEDs together that weren't meant to be connected.

8. Then I set up the regulator so that the flat side matched with the shaded flat side on the circuit board in spot VR1. Then I soldered the component.

9. I set up the trimmer in spot RV1 and soldered it. Then I pushed the corresponding knob on top of the trimmer.

Work on the LEDs
Solder the Power Jack

10. I then set up the 3 push buttons into spots SW1, SW2, and SW3 and soldered them.

11. Set up the IC dip (socket) so that the crescent on one side of the dip lined up with the side with the "1" next to the IC1 spot. This is incredibly important, since otherwise the circuit will malfunction. Solder the IC dip so that none of the prongs are soldered together. Also, it is very important to make sure you are orienting the IC the exact way the instructions tell you. If you don't, the circuit will not function properly.

12. Solder the Power Jack into ‘SK1’. Make sure you solder the metal prongs from the side to the neighboring metal wires/solder-holes.

13. Screw the battery pack in on the backside of the board. Then solder in the battery pack so that the red lead is soldered to the metal square reading red and the black lead to the metal square reading black.

14. Finally, glue in the red display so that the red screen covers the LEDs.

Solder in the battery
Complete the kit

15. When you insert the batteries, the LED scroller should read: ‘I ♥ minikits’. Hold the ‘Set’ button to determine a message. Then choose a character by selecting it with the up and down buttons. Press Set to move to the next character. Finish the scrolling text by ending with the ‘<’ sign.

16. You can adjust the scrolling speed by turning the 'Speed' knob. You can also put the message into standby mode by pressing the ‘Stby’/up button.

17. Enjoy!

Tips and Tricks

Whenever I solder, I try to use a simple technique that greatly simplifies the soldering process. I always hold the spool in my left hand (or right hand if you're left handed), and straighten out about 4 to 5 inches of wire. I then grab the soldering iron. I use the straightened solder wire to touch the base of the hole of whatever component I'm about to solder. Then I touch the soldering iron to the end of the wire so that the wire melts around the base. This way the solder doesn't splatter or touch neighboring holes. Less solder wire is consumed and it also looks neater.

Always try to set up and solder similar components (such as a single value of resistor or a diode) at one time. Do not try to solder all the different values of capacitors or resistors at one time. Do one value at a time.

Pay careful attention to components that have an assigned polarity (+/-) (such as diodes, certain types of capacitors, and LEDs). Getting these polarities wrong could potentially disrupt or destroy the circuit.

Don't solder all the LEDs at once. Doing so will make it tougher to solder as well as increase the chances of accidentally getting the polarities wrong.

Whenever you use an IC, always solder in an IC socket before implementing the IC.

Make sure that every IC used is oriented correctly.

Error Bugging/Troubleshooting

After completing the kit, I plugged in the battery only to find that it didn't work. Annoyed, I picked up the kit and came across a nice little surprise: one of the components was blazing hot. I then unplugged the battery and tried to search for the source of the error. What error was causing the circuit to short? I ran through my typical procedure because a multimeter wasn't handy.

1. I checked to see if all the components were in the right place. Check.
2. I checked to see if this error would occur if the battery polarity was switched. (it didn't). Check.
3. I checked to see if the LEDs were oriented the right way. Check.

Still, the circuit didn't operate. What was going on? In defeat, I then looked at the case. Something was off, something small. I couldn't put my finger on it. And then, I realized the IC was backwards! It was a very small, barely noticeable mistake, but integral to the circuit. Fortunately we used an IC socket, so correcting this error was simple. I pulled out the IC and switched it around and it worked!
Ben Adler is currently a first year at Rice University. While generally undecided about his major, he plans on majoring in some type of science or engineering. He is an audiophile and loves to recycle unwanted speakers, making his own speaker systems.