Multi-Line Telephone Intercom
element14 Presents | Derek Brodeur's VCP Profile | Project Videos
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Modern smart phones have become so ubiquitous these days that old analog phones are getting left in the dust. However, you may still have a few of these old phones hanging around your house collecting cobwebs or you may have seen some lingering on the shelves at your local thrift shop. Now’s your chance to put them to good use. In this video, Derek takes you back to a time when stretching a phone cord across the room was the norm by creating a 4-line telephone intercom system with basic ringing capability. The circuit surrounds a DTMF decoder IC which handles keypress detection, a simple AC inverter to handle the ringing and a current source which allows analog communication between multiple phones. |
Bill of Materials
| Product Name | Manufacturer | Quantity | Buy Kit |
|---|---|---|---|
| 0.1uF 25v Capacitor | 5 | Buy Now | |
| 1uF 50v Capacitor | 2 | Buy Now | |
| 20pF Capacitor | 2 | Buy Now | |
| 2.2uF 250V Capacitor | 1 | Buy Now | |
| 1N4001 Diode | 5 | Buy Now | |
| IRF540N N-Channel MOSFET | 2 | Buy Now | |
| 2N2904 NPN Transistor | 5 | Buy Now | |
| HT9170D DTMF Decoder | Holtek | 1 | Buy Now |
| CD4047 Multivibrator | Texas Instruments | 1 | Buy Now |
| DC/DC Converter 5v / 1A | RECOM | 1 | Buy Now |
| LM317T Adjustable Voltage Regulator | ON Semiconductor | 1 | Buy Now |
| 3.579545MHz Crystal | ABL | 1 | Buy Now |
| DPDT Relay | OMRON | 5 | Buy Now |
| 75k 1/4 Watt Resistor | 1 | Buy Now | |
| 220 Ohm 1/4 Watt Resistor | 2 | Buy Now | |
| 22 Ohm 1/4 Watt Resistor | 1 | Buy Now | |
| 56k 1/4 Watt Resistor | 2 | Buy Now | |
| 100k 1/4 Watt Resistor | 1 | Buy Now | |
| 150k 1/4 Watt Resistor | 1 | Buy Now | |
| 68k 1/4 Watt Resistor | 1 | Buy Now | |
| 1k 1/4 Watt Resistor | 5 | Buy Now | |
| 300k 1/4 Watt Resistor | 1 | Buy Now |
Additional Parts:
| Product Name | Quantity |
|---|---|
| RJ11 Telephone Jack - right angle | 5 |
| 120V / 18V Center Tap Transformer | 1 |
| Prototyping PCB | 2 |
| PCB Standoffs + Screws | 4 |
| Metal Enclosure | 1 |
| SOP-20 Breakout board | 1 |
| Derek Brodeur - Schematic.pdf |
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