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| Neverending Project:
This question is not specific to arcade controls, so it may not belong here. It probably doesn't even belong on this forum, but since I frequent this forum (and I like the community) I thought I would give it a try. A few weeks ago I built my kids a rocket ship in their playroom. And what rocket would be complete without a control panel? So I will be making some sort of instrument cluster comprised of leftover arcade pushbuttons and joysticks (aha! a link to this forum!). I have this idea of making a picture of an instrument gauge, and then putting LEDs around the outside like the numbers on a clock. In the middle I want a dial that as you turn it up, the LEDs will light in sequence - similar to a power meter. So I googled around a bit and came across the LM3914 IC. It seems perfect for my application. Basically it has 10 current regulated output pins that drive LEDs based on an input signal of 0-5V. The chip takes care of the 10-step voltage divider and the current limiting and everything. It can even be set to output a bar style or a single light at a time. Great, so now I need to figure out out to take my input voltage (11.5V from a wall adapter) and make a 0-5V range, controlled by a potentiometer so I can make my gauge work. I also came across the LM317, which is an adjustable regulator. There is an example circuit to output a voltage range from 1.5V to a little less than the input voltage. I can modify this circuit to give me a range of 1.5V-5V, which is almost there. So now (finally) my question. Is there an easier way to do this? Is there an obvious way to get a variable voltage from a 11.5V source from 0V to 5V? Has anyone done anything similar? |
| SavannahLion:
Is the wall wart going to be driving anything else besides this circuit? |
| RayB:
My guess is you need a resistor to bring the maxium down to 5v. THEN add a potentiometer (or variable resistor) to handle the remaining 5v to 0v |
| Neverending Project:
Short answer: yes. I forget the current rating of the wall-wart, but it was my intention to have at least two of these "instrument gauges" hooked up to the wall wart. And throw some additional push-button controlled LEDs into the mix as well. So I would take the +11.5V input and feed it to the VCC of two LM3914 chips, as well as any additional LEDs I hook up (a few). If the wart I have is not regulated, I guess I will need a little voltage regulating circuit on the VCC rail as well. I plan on making sure it has enough current to drive it all, but all I am really driving is LEDs so it shouldn't be too bad. |
| Neverending Project:
--- Quote from: RayB on July 10, 2008, 01:19:44 pm ---My guess is you need a resistor to bring the maxium down to 5v. THEN add a potentiometer (or variable resistor) to handle the remaining 5v to 0v --- End quote --- It was my (basic) understanding that adding a resistor to the input voltage will reduce the current available, not drop the voltage, right? |
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