Okay, got a question. I'm working on a 10 band spectrum analyzer based of the Velleman K4300 (which has been discontinued). Anyway, I modified the schematic to work with an LM3914 for the bargraph display. My questiuon is do I really need R2 and R3 in this diagram, and if so, how might I go about calculating their values?? Click for larger sized pics Thanks in advance Filter Board LED Board The switch is there so that I can change modes on the fly from dot to bar mode. Also, do you all think that I could hook a pot to the LED board to adjust the peak of the lights?? Maybe it would hook to pin 6 (RHI), not sure about that.
You've got the LM3914 set as a 1.2v FSD meter, so R2 and R3 are needed to scale your peak input voltage down to 1.2v. It's a simple potential divider, but might be easier to use if you make one a preset, or use one preset instead of both with the wiper to pin5. You've got the led current at 18mA with R1=680R, (equals 12.5/R1), you can vary it by making R1 about 470R and adding a 2k preset.
Not a problem, I can figure that out with a multimeter and some math. Not sure exactly what you mean there. Are you saying that I should only use one resistor rather than two?? Please explain what you mean by preset and wiper... I'm still learning, slowly but surely. Also, the original schematics can be found here if you want to take a look at what I've done. http://www.animeguru.com/schematic/schematic.html The original schematic called for a 1K5 for R2 EDIT: I'm also looking for a good book on this stuff, so far I've been using the net, but a good basic electronics book would be useful.
Like macroman's mod of a 2-resistor circuit in a recent thread here : A pre-set is a small variable resistor with a screw-slot to adjust it rather than a knob. The preset acts as two resistors, as you turn the dial (the wiper arm), one goes up, t'other goes down, so it divides the incoming voltage to the level you want - same as a volume control. Datasheet shows 1k2 for R1 to give 10mA led current, ample for most needs. 1k5 would give 8mA, only marginally less bright. With a battery supply you'd probably go even lower.
