Hello guys! I'm here again with another simple mod to share with you, for SIM900A mini gsm module. Actually I have no idea about the prices of these modules, but the one I could find in our local market was this 'mini' type. The difference was that it lacked the two ports for mic in and speaker out. Though I needed those two, I couldn't afford to buy another module just for those ports. While surfing through these various gsm modules, I saw that SIM900A as well as the SIM900A mini model I had were based on the same SIM900A IC. So I thought... "Why not try to add the missing features myself instead of buying a whole GSM module??? ;-) "
So, let's go...!!!!
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Step 1: SIM900A IC.....
Well, so here's it! This is the IC on both models. So it must be possible to add mic and earphone to it. Let's check out this IC's pin-out!
Step 2: Identify SIM900A IC Pinout...
So let's identify SIM900A pins. As you can see in the image, you can see there are 2 pins for mic in as 'MIC_P' and 'MIC_N'. MIC_P means mic positive and MIC_N means mic negative. Similarly you have 2 pins for earphone out as 'SPK_P' and 'SPK_N'. They are SPK_P for positive of speaker and SPK_N for negative of speaker. Actually this polarity doesn't matter as I think, correct me if I'm wrong, and it didn't matter with me.
Ahh... forgot to tell.....
There you have 2 more pins for line in also. If you need these, may be to listen to a song from dialling a number, use these pins too!! ;-P
Step 3: Solder Connections!!
So that now we have identify which pins we need, it's time for the mod! You can add female audio jacks as i have shown in the diagram, but I was too lazy for that, and I even didn't want a speaker, so I just soldiered a mic directly to the board. Actually soldering components directly to an IC is not advisable as it can ruin your IC if it gets over heated. But I noted that the IC was on something like another PCB, so I thought I would not ruin my module!! ;-)
Then you'll see my module with mic soldered, and you can actually add 3 female audio ports as I said earlier.
Step 4: Finish Up!
So that's it guys! Feel free to comment your thoughts and I like if you comment your ideas..............