davekra

Thanks Audioguru, I put it together like your drawing and it works great. As far as the regulators, I was just trying to keep the thing as cool as possible. It's going into a space without much air movement. I'll be putting a heat sink on it when it's done. Now I just have to put it into a nice box and install it. Thanks all for your help. davidk

Ok, I tried using an LM324 as a pulse width modulator to control the voltage to the led's through a transistor. This does work however as more led's light in bar mode the brightness changes. Is this not a good way to control the brightness? Why is the brightness going down as more led's light up? With 30 led's on full it's drawing about 680ma. Another question is can I hook two 5volt regulators in parallel? Will this distribute the load to both regulators? Thanks, davidk

Thanks MP, Last nigt I found that if I put a 2K resistor and a 100K pot between pin 7 and ground I got brightness control with a full sweep of the pot. The circuit is turning out to be a lot simpler than I thought it would be. No op amp needed and whatnot. I still have the question about having a single brightness control for all chips. I trid to tie all the pin 7's through one resistor but no dice. I also tried to put a diode between each pin 7 and the resistor but again nothing. I'd really like to have one adjustment for brightness, can anyone sugest a way of wiring it? Thanks, davidk

I think I got the pots setup correctly. I found I needed to put one side to + and the other to - with the wiper going to the signal in of the chips. Theres still the question of brightness control. Can it be done with one adjustment? Thanks, davidk

I've been looking at resistor networks and it seems any thing over 2 or 3 resistors and it gets verrrry hard to calculate. So how bout having separate pots for each voltage needed? I modified my drawing showing 5 pots to set the hi and lo voltages for each chip. Will the separate pots idea work? How bout the brightness control? Is there a way to control the brightness for all chips with one adjusment or will the circuit in the box work for each chip? Thanks, davidk

I'm sorry, "dividing the output of the transducer" may have been an incorrect phrase. I'm passing the output directly to each chip and trying to set the Rlo and Rhi to give me what I want. I re-read the datasheet aloud to my disinterested wife and realized I was skimming over some important information when I read it to myself. :-[ The datasheet said to ground pin 8 and place a resistor from pin 7 to ground. I've put together a crude drawing of the circuit as it stands now. I've got the thing working sort of. I'm still trying to figure out the correct values for resistors R5 - R10 but it's displaying the way I want. For the brightness can I just put in the circuit, in the box on my drawing, in place on pin 7 and 8? What values could I start with for the resistors? Is there a way to control the brightness for all chips with one adjustment? Thanks allot for your patience and help. davidk

Hi, I'm trying to use 4 lm3914 for a preasure gauge using an mpx4250a transducer. I'd like to have the first ten led's setup for dot mode from a voltage of .2 to 1.7. The remaining 30 led's would be setup for bar mode from a voltage of 1.7 to 3.2. I'd also like to be able to adjust the brightness for the entire display. I’ve been able to hookup the chips to give me the dot and bar that I want but I'm having trouble with the signal input to each chip. I can’t figure out how to divide the output of the transducer and have a brightness control. I’ve tried to figure out the resistor values but can’t seem to get the calculations to work. Would anyone be willing to help me figure out how to hook this up? Both the configuration and some approximate values for things? I can play with the values if I have the schematic, I just cant seem to put it all together. Thanks, davidk