Hello
I have some questions about a dot matrix display that I am trying to develop. I am using an 8x8 dot matrix display. I have two ways to display the required text, one is by using ICM7218AIJI chip, the other is to write my own logic and design a circuit which does it. I have done both of them with obvious trade offs:
- By using 7218 I have a dedicated dot matrix refresh utility which makes it more bright, reduces the area of PCB (PCB design area and manufacturing cost are the most important factor in my design), reduces load on the microcontroller, but it is not more suitable for scrolling options than a dedicated logic. 2. While designing dedicated hardware, I have actually used decoders and ulns for grounding and a scanning function designed in the microcontroller. The number of chips is huge and ofcourse results in large area for PCB, not to mention since the scan time is very small for each row or column, the applied voltage increases drastically. Surprisngly however, the chips used are cheaper than a 7218 counterpart for each dot matrix.
My questions are as follows: 1. Are there cheap 7218 resellers in China and Taiwan etc. which can provide good quotations on bulk orders (say 100 pieces to start with?) 2. Does 7218 have an internal current limiter? I have given it
100mA, 150mA and 200mA, and each time it has resulted in increased brightness, does it even have a current limiter, or is it designers job to limit current on the chip?Thanks in advance
Mak