Hi all, I am new here. I found this site, when looking for more info on cascading LM3914's to drive a 20 segment LED display. The link to the thread I found via google is here: link and it did help me understand better, but I am hoping someone can take a look at the display driver portion of this schematic and tell me if I understood correctly. The project is for a LED tachometer, what I am shooting for with the LM3914's is 0-8V range which should correspond well with the 0 to 8000 RPM signal from the LM2917M IC. The data sheets for the LED drivers are very confusing (at least to me) when it come to cascading the chips. If someone has a moment, please let me know if I did it correctly. I was thinking of just buying livewire to simulate it, but after finding the prices for it, I just can't afford it right now. Thanks in advance for your time. Here is a picture of the schematic. Link for full scale picture: Clicky Thanks folks, Jason
I ran into the same problem during my electronics coursework, got it all explained here Link. Moriquendi
Thanks, I just read through that link, and if I am reading it correctly, I have got it right, with the exception of the resistor from between LED 9&10 to pin 11. It took much grinding and gnashing of teeth to get this far. I was beginning to wonder if designing a inexpensive LED tach was worth my time or not. BTW, I have absolutely no formal electronics training. It is just something I find of interest and am trying to teach myself. My other current projects include a bargraph fuel level gauge, and a Mosfet winch control for running a Vehicle recovery winch. That project is 90% complete, and should be capable of bi-directional control of ~500 amp 12VDC load at full capacity of the winch. The last thing I have to tie that one up is mounting my parallel hexfets to a solid copper buss capable of handling the current draw, and of course an enclosure and heatsinking. Later, Jason
Of all the ICs I've used the LM3914 has to be the hardest, that includes PICs and CPLDs. I dont know why it is but I find the datasheet hard to understand. Best of luck with your projects, one thing I would mention because I stumbled over it is that if you use a relativly high voltage to run the LM3914 and have high current LEDs the chip will get very hot, I had to add a separate 5v powersupply to my project just to drive the LM3914s and LEDs so that they didnt fry. Moriquendi
Thanks for the info about the supply. I have a few 7805 regulators around, I guess I will incorporate one when I build it. Thanks, Jason
