Serial 4-Digit 7-Segment LED Board - Assembly Instructions
Use the following photo as a reference as you assemble the LED-4x7 board.
Parts List (All parts are available at JRHackett.net)
| Label | Description | D1 | Diode, 1N4148 |
| R1 | Resistor, 47k, 1/4 Watt |
| R2, R3 | Resistor, 4.7k, 1/4 Watt |
| R4 | Resistor, 100k, 1/4 Watt |
| Program Adapter | 4-Pin Rt-Angle Female Header |
| Breadboard Adapter | 5-Pin Rt-Angle Female Header |
| C1 | Capacitor, .01 µF Ceramic |
| C2 | Capacitor, 10 µF Electrolytic |
| 08M | 8-pin IC Socket and PICAXE-08M |
| MAX7219 | 24-pin IC Socket and MAX7219 |
| None | 5x2 Straight Male Header (Optional) |
| None | Two 6-pin Straight Female Headers (Optional) |
| None | 4-Digit 7-Segment LED Display |
Assembly Instructions
The LED-4x7 PC board is very easy to assemble. As usual, it's best to proceed from the smallest to the largest parts. The order of the parts in the Parts List is arranged this way, so just work your way from the top of the Parts List to the bottom. The only exception to this order are the optional 6-pin straight female headers. Since these headers are inserted from the bottom of the board and soldered on the top, it's best to leave it until last. That way, the bottom of the board can be more easily cleaned before soldering the two 6-pin female headers (if you are using them).
When you have installed all the parts in the Parts List (except the 6-pin female headers), cut a piece of jumper wire, remove its insulation, fit it tightly over the Breadboard Connector and down through the two holes on each side. Hold it tightly in place with a small clamp and solder the ends to the bottom of the board. This wire has no electrical function; it simply protects the Breadboard Connector from the stress of multiple insertions and extractions.
When all the parts (except the two 6-pin female headers) have been soldered in place, make sure all the excess leads have been clipped from the bottom of the board. At this point you may want to rub the bottom of the board a few times on a piece of emery-type sandpaper to remove any sharp edges. You can use flux remover and a tooth brush to clean the bottom of the board, but I have found that ordinary paint thinner works just as well for this purpose and it's easier on your hands. Once you have cleaned the bottom of the board, you can install the two 6-pin female headers on the bottom and solder them in place on the top of the board. If you prefer, the LED display can also be directly soldered to the PC board without using the two 6-pin female headers. However, any soldering problems on the board in the area underneath the LED display could result in having to de-solder the display in order to be able to correct the problem.
Testing the Completed LED-4x7 Board
To test the completed LED-4x7 board you will need either the UPA-4x4 or the SUPA-4x3 programming adapter (or a stripboard equivalent). If you have been following the PICAXE Primer column in Nuts & Volts magazine, you probably already have a suitable adapter - just make sure the pinout matches that of the adapter on the LED-4x7 board. The following photo shows the SUPA-4x3 inserted in the LED-4x7 Programming Adapter connector. The painted dots on the SUPA-4x3 are a simple mnemonic color-coding scheme I use to know which pin is which [Ground = Black, Sin = Green (because it's "in" to be Green) and Sout = Yellow (because you "yell" out). You can laugh if you want, but it works for me! :-)
The following programs can be used to test and configure the completed LED-4x7 board. You can click on any program name to view and/or download it. If you want more information about any of these programs, you may want to obtain a copy of the PICAXE Primer articles I mentioned earlier. If you don't already subscribe to Nuts & Volts magazine, you may want to do so because subscribers have free access to previous issues back to January of 2004.
The completed LED-4x7 board can be tested by downloading the LED47Count.bas program to the on-board 08M. For this purpose, you don't need a second processor on the breadboard; just make sure the LED-4x7 board is powered and use the SUPA-4x3 programming adapter (or any adapter with the same pinout) to download the program to the board. If everything is working correctly, you will see the display counting from 0 to 9999 repetitively.
Installing the Serial Driver Software
When you are sure that your LED-4x7 board is functioning properly, you can install the LED47Driver.bas software using the same procedure we just used to test the board. Next, set up a simple breadboard circuit similar to the one shown in the photo above and download the CountToLED47.bas software to the 08M processor on the breadboard; you should see the same count as before. The difference is that, this time, the 08M on the breadboard is doing the counting and sending the numbers to the LED-4x7.
If you look at the CountToLED47.bas program, you can see that it sends four bytes of data at 4800 baud for each count. To use the LED-4x7 board in any of your projects, you just have to do the same thing: Always send data at 4800 baud in groups of four bytes and include a small delay between each transmission so that the LED-4x7 can keep up with the incomming data.
If you have any problems getting your LED-4x7 board to function properly, email me at Ron@JRHackett.net and I will do what I can to help.