Invention Lab — Powered by RadioShack®

Every hobbyist needs one of these; an ATX power supply made into an inexpensive ben top power supply. Capable of supplying a number of voltages, this simple project will be a center piece for any do-it-yourselfist needing a solution to their power needs in testing and fabricating other projects.

On a standard ATX power supply, the PS_ON pin can be identified by the green wire, number 16. When a computer is turned on, this pin is tied low and gives the PSU a signal to turn on its main voltages. Prior to activating the main voltages, pin 9 being +5VSB and purple, provides a constant +5VDC as a standby voltage and can be capable of delivering an amp or more while main voltage is off. It may be useful as an indicator of AC power or an always-on supply for small loads. Other voltages provided include +3.3, +5 main, +12, -12, and -5. Combining these will yield various other voltages that can be calculated by absolute potential.- ted

This was easily a weekend project, and RadioShack had all the components. A phone line gives about 48vdc, with red being positive. Some older houses have mismatched wiring with green positive and some newer have digital signals carrying multiple lines on the same two wires. This project targets those with plain copper wire, on a single line, looking to feel like a fancy corporation with the phone gadgets. The action of ‘hold’ on a phone line allows the disconnection of all handsets, but keeps the line open and the end-user able to receive whatever we pipe in. A 330ohm 1/4 watt resistor in parallel with the phone line, acts as an active handset and allows enough current through to prevent the phone company from hanging up the call. With the line still open, we are able to inject linear audio from any source. This audio is heard by the end-user, and by us if our handset is still active.

Converting linear audio to ‘phone grade’ audio requires an isolation transformer between the audio source and phone line. A 47uf electrolytic cap gives plenty of filter buffer between the linear source and input. The transformer is non polar, though be sure the coil connections are paired as on the schematic. A 3.5mm headphone jack is our audio input source. Any form factor input connector can be used, though the most common connector for audio these days is the 3.5mm; a jack was used to simplify the design and keep all components contained. - ted

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