This article is part of the PCB Giveaway program that we have running here at Youritronics. Morgoth will get a free pcb manufactured by BKRtech for submitting this project. If you’re interested in participating, read more on the program page.
These days most pharmacies use LED pharmacy crosses posted at their entrance to let people know there is a pharmacy there. The reasons are obvious, they look cool&hi-tech, they can be seen from distance and they can be customized really easy (well, easy customizing pretty much depends on how the manufacturer approaches things).
If you try to search the web about schematics or example codes for this kind of circuit you wont find any, and again i think the reason is obvious, the crosses are quite expensive and so is the profit for the manufacturer. So nobody is gonna post schematics for such a project, unless you’re a hobbyist and you’re having fun with electronics.
The project consists of one ATmega64, three ULN2003 and five 5×7 LED matrix from Kingbright(TA20-11EWA). I had the idea to build something like this but so far i haven’t had the time nor the knowledge to get it done. So i asked Morgoth if he would like to participate in the project. I sent him the LED’s, the drivers and the PCB and he started working. As you can see not many parts are involved , but the secret lies in the microcontroller, it’s the programming that does the job.
In the next pictures you can see the microcontroller board with the ULN2003 darlington arrays:
The circuit was designed to receive messages trough serial interface from a computer and than display them. Morgoth also designed a custom terminal for windows which provides easy access to the display.
In this test phase a serial interface by wire was used to transmit data between the terminal and the ATmega64, but a wireless or bluetooth module could be integrated with no problem.
Also as a note, the LED’s don’t light up really bright, for that to happen you need to use drivers on the positive rail. This also applies if you’re planning to take the project to another level and use bigger LED’s
And now, watch some videos with the LED Pharmacy Cross beeing controlled from the computer: