Editing Cellular Rotary Phone
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===Project Scope=== | ===Project Scope=== | ||
− | <b>Description:</b><br> This is a deeper look into the Port-O-Rotary phone. We stuck the GM862 | + | <b>Description:</b><br> This is a deeper look into the Port-O-Rotary phone. We stuck the GM862 cellular module into an old rotary phone enclosure, and viola, it was an instant, ridiculous, hit. |
Here we are going to breakdown the schematics and systems of the rotary phone. | Here we are going to breakdown the schematics and systems of the rotary phone. | ||
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===Power=== | ===Power=== | ||
Really simple - the GM862 requires 3.8V and a Lithium Polymer outputs 3.7-4V. No regulator needed, but we will need a charger. We currently use an external charger from a third party company. Aubrey noted the GM862 has a built in Lithium-Ion charger that may work, we haven't tested it yet. Ideally we would stick a barrel jack in the back of the enclosure where the RJ11 telephone jack used to reside. Anyone have any recommendations? | Really simple - the GM862 requires 3.8V and a Lithium Polymer outputs 3.7-4V. No regulator needed, but we will need a charger. We currently use an external charger from a third party company. Aubrey noted the GM862 has a built in Lithium-Ion charger that may work, we haven't tested it yet. Ideally we would stick a barrel jack in the back of the enclosure where the RJ11 telephone jack used to reside. Anyone have any recommendations? | ||
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===Rotary Decoding=== | ===Rotary Decoding=== | ||
We use a PIC 16LF88 (remember we are at 3.7V! We need a low-voltage PIC!) to read the hook and rotary. Pretty simple switch decoding routine. We just read the opening/closing of the paddles behind the rotary. There are two - one set of paddles opens and closes for each number that passes by, the other set of paddles is normally open when the rotary is in the home position and closed while the rotary dial is moving. Reading this second set of paddles will tell us when the dialing of a single number is complete. | We use a PIC 16LF88 (remember we are at 3.7V! We need a low-voltage PIC!) to read the hook and rotary. Pretty simple switch decoding routine. We just read the opening/closing of the paddles behind the rotary. There are two - one set of paddles opens and closes for each number that passes by, the other set of paddles is normally open when the rotary is in the home position and closed while the rotary dial is moving. Reading this second set of paddles will tell us when the dialing of a single number is complete. | ||
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Here's the good stuff. Well, it will be here once I can get to the updated schematics. | Here's the good stuff. Well, it will be here once I can get to the updated schematics. | ||
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===Audio Considerations=== | ===Audio Considerations=== | ||
We hooked the handset mic and ear-piece directly to the GM862 without any external components. The mic was biased through a 10k resistor using the 3.7V off the battery. One would think that this would be a clean source of DC power, coming directly off a high current battery. In practice however, there is some horrendous buzzing in the ear piece. Funny thing, when we disconnect the mic, all the buzzing went away. | We hooked the handset mic and ear-piece directly to the GM862 without any external components. The mic was biased through a 10k resistor using the 3.7V off the battery. One would think that this would be a clean source of DC power, coming directly off a high current battery. In practice however, there is some horrendous buzzing in the ear piece. Funny thing, when we disconnect the mic, all the buzzing went away. | ||
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[[Image:GM862-Mic-circuit.jpg|400px]] | [[Image:GM862-Mic-circuit.jpg|400px]] | ||
− | Here you can see a mildly complex electret mic biasing circuit. What is this? Well, an | + | Here you can see a mildly complex electret mic biasing circuit. What is this? Well, an electret mic needs just a little bit of current to operate. Normally you can power the mic by just attaching one side to a 10k pull-up resistor. This circuit takes the 3.8V main power, and outputs a super clean 3V to biasing the mic. Perhaps getting rid of all the RF noise that the GM862 is putting onto the main power? No way! REALLY!? It works great. Why didn't we think of this before!? We use a basic 3.3V regulator and a couple caps and it works just as well. You ''can'' power the mic using the main 3.8V power, but expect some buzzing. To get rid of the buzzing, send that main voltage through a simple 3V or 3.3V regulator circuit and you'll be very happy. |
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===Board Layout=== | ===Board Layout=== | ||
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The PIC is connected to GM862 in various ways. Obviously we need TX and RX to send commands and receive ''OK'' responses. The PIC also monitors the RI (Ring indicator) line, as well as controlling the On/Off line to turn on the GM862 (requires a 1-2 second pulse) when the board is powered up. The PIC controls the p-channel MOSFET to power the external ringer board and toggles the ring pins to get the bells to activate when the RI pin is fired (I forget if it's active high or active low...). | The PIC is connected to GM862 in various ways. Obviously we need TX and RX to send commands and receive ''OK'' responses. The PIC also monitors the RI (Ring indicator) line, as well as controlling the On/Off line to turn on the GM862 (requires a 1-2 second pulse) when the board is powered up. The PIC controls the p-channel MOSFET to power the external ringer board and toggles the ring pins to get the bells to activate when the RI pin is fired (I forget if it's active high or active low...). | ||
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<b>Supplier Info:</b><br> | <b>Supplier Info:</b><br> | ||
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<b>Related Items:</b><br> | <b>Related Items:</b><br> | ||
[[GM862 Cellular Module]] | [[GM862 Cellular Module]] | ||
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