Interfacing Aerocomm AC4790 with Propeller Chip – Hardware Perspective

In this post I will attempt to describe how I built a simple carrier board for AC4790 and then interfaced that with my Propeller chip (that is mounted on a Propstick). To get an introduction to what and why of AC4790, please see my earlier post here.

So, as stated in my last posting, AC4790 has 20 pins. Of course, for my application in ALIBE, I will only need for the communication module to be “reactive” vs “proactive” – meaning, the Command Center in homebase will issue a command to ALIBE’s communication module (AC4790) and then will expect ALIBE to either return data back to it or take an action onboard ALIBE. This is what I define as “reactive”. Proactive would be when the communication module would proactively send data to the homebase – ie., without being “asked” for.

In this scenario, I only need to tap into a few pins off the 20 pin lot. Here’s the description of these pins (as I said in my earlier posting).

1 (Session Indicator),
2 (Tx – from Propeller to AC4790 device),
3 (Rx – from AC4790 device to Propeller),
5 (GND),
9 (Rx Indicator),
10 and 11 (both need to be 3.3v VDD). and that’s it. 

I needed pins 1 and 9 for my LEDs (pic below).
My carrier board (very simple one BTW), has soldered LEDs and also exposes the pin 1 and 9 (as pin 1 and 4 carrier board) – if in case I need to further use those pins for future work. I am happy w/ the way it turned out.

Read thru the AC4790 manual especially the Pin characteristics and their meanings. Understanding this will be very helpful – it is only 2 pages long.

I used one of those PCB’s from radioshack and soldered in 7 pin SIP into the board as seen here underside of the PCB: There’s some additional soldering outside of just the 7 SIP pin. We’ll get to that soon.

I found some old connectors from my parts treasure chest and repurposed them to connect the AC4790 with the PCB. The wires are soldered on the underside (above picture) . You can see that here. Take a note of the pin numbers and ensure you are using the right pins and connecting the right pins to the SIP pins. Incorrectly hooking them up WILL for sure fry your AC4790. And, you don’t want that!

I have highlighted the pin layout on AC4790. Pay close attention to the numbering.

This is probably a good time to look at this wiring diagram – it will give you an idea of how simple this is. Also, note that I hooked up my 2 LEDs to the pins 3 and 9 for the Session and Rx indication. They can be very useful to visually see what’s going on onboard ALIBE during communication. Note how pin 10 and 11 are together hooked up to 3.3v Vdd. This is important to know that AC4790 is a 3.3v device and NOT a 5v device.

The completed PCB looks as here. I also added a small piece of foam btwn the AC4790 and the PCB.

I then took my “finished” product to my breadboard and hooked up the AC4790 Carrier Board (CB) to my Propeller pins. As you can tell from this picture, I only need 3 pins on Propeller to make my communication module working. Pretty cool ah!

The best part about this CB design is that I can always unplug the connectors to the AC4790, unscrew the standoffs, and take the AC4790 to my devboard if in case I need to edit its EEPROM settings or do a “dev board to dev board” testing. Very flexible – works well for my project.

Look for the following posting on how I tested this setup.

ciao
Nagi