|Published (Last):||13 July 2011|
|PDF File Size:||13.21 Mb|
|ePub File Size:||4.14 Mb|
|Price:||Free* [*Free Regsitration Required]|
Can't figure out why. Pages: . Topic: Using a LS 7-segment driver, but doesn't work. Read times previous topic - next topic. Using a LS 7-segment driver, but doesn't work.
Hi all, I'm building a project where I want to use two double-digit 7-segment-LED displays green, common cathode. My problem: I can't get the LED segments to light up properly. When I connect using the driver IC, the segments light up only weakly it's visible in the pics, but worse in real life.
My bench power supply indicates the circuit is using 9 mA. That works beautifully, using up more than three times the power: 30 mA according to my bench power supply: I've made a quick schematic, maybe it'll help: Does anyone here have any clues or tips? Now with Unlimited Eagle board sizes! Re: Using a LS 7-segment driver, but doesn't work. Does the display really have 4 LEDs in series like that?
That would seem to require more than 5V to turn them all on. Hi, Those tiny displays will not have 4 leds in series, that's a bad choice of symbol. I believe the problem here is your choice of display and driver chip. You are using common cathode displays, and therefore your chip needs to source current to the segments.
Problem is, if you look at the data sheet, 74ls outputs are not meant to drive the display directly, but via transistors it was originally designed for lamps There is an internal 2.
Your idea would have worked ok with 74ls and common anode displays. You would be much better off with a max! It could drive all 4 of your digits with minimum external components and only 3 Arduino pins.
Alternatively, drive the displays with the Arudino and 4 npn transistors like this. Quote from: vincentjacobs on Jul 05, , pm.
Dt Sheet. NSC 74LS The device should not be operated at these limits. Note 2: Not more than one output should be shorted at a time, and the duration should not exceed one second.
74LS248 View Datasheet(PDF) - Texas Instruments
The LS is a pin version of the pin LS49 and includes full functional capability for lamp test and ripple blanking which was not available in the LS The composition of all characters, except the 6 and 9 are identical between the LS, , and the LS47, 48 and The LS47 thru 49 compose the and without tails, the LS thru compose the and with the tails. The LS has active-low outputs for direct drive of indicators.