The 15 Switch (Button) to 4-Bit Decoder was originally designed to reduce the number of IOs needed for a LED Commander switch inputs. Since the Led Commander has a fixed number of IOs which are used both as input triggers and LED circuit controllers, if we reduced the number of IOs needed for triggers, it would allow more IOs for LED circuit control. So this device can take one of fifteen switch-inputs and translates it to a four bit binary number. This reduces the number of IOs needed for fifteen switches to four. Click on image for closer view.
Turns out, this is useful for other devices as well. For example, the Alcorn McBride 7400 mpeg player and the Pioneer DVD 5000/8000 (and older 7200/7400 series) can be set up for button input control. All of these devices only use four IOs interpreted as four-bit binary number to determine which of 15 videos will play. Alcorn suggest the user build a diode matrix to accomplish this decoding. They even provide a circuit design in their manual for a diode matrix. There are several issues with the diode matrix. The first is you need to use high quality diodes to ensure your circuit is not affected by leakage current that will corrupt the diode logic output. That is a solvable problem. The second is not: you cannot predict what the output will be if more than one button is pushed at a time. This means that for certain button combinations neither of the single buttons’ code will be on the output, but another code altogether. Our switch decoder has a built in priority function which ensures the highest button is the one that will have its results put on the output IOs. This ensures that users cannot get strange results from simultaneous multiple-button pushes. Finally, a diode matrix can be unwieldy to fabricate and difficult to hook external wiring.
Another application is to increase a NetLinx IOs. With this device you can give four NetLinx IOs contact closure that is decoded for one of fifteen switches. That’s a lot less expensive than adding another two NXC-IO10 Cards or a CPI16 card.
The 15-Switch Decoder can be fabricated to use its own dedicated power supply. It can also be constructed to use 9-12vdc power from another device or be a parasitic load on a 5 vdc, TTL, power supply. For example, the Alcorn mpeg player can supply the voltage needed by the 15-Switch Decoder. You could also use NetLinx’s 12 volt power supply to power it.
- 15-Switch Decoder (without PS) $75