Sweeping indicator - Page 1
Forum section: electronics / beginners

author: NOKA
author_rank: Newbie
timestamp: December 05, 2019, 03:40:00 am
content: Hi!You can skip this paragraph>>I am a long time follower but only recently registered. Some of you have helped me with previous projects such as my bike light for physics in grade 10. In any case, I’ve decided to do another project and i think I’ve bitten off more than I can chew.The project I am working on is a sweeping indicator. (If you don’t know what that is, just goldgelb audi-indicator). I have created one using Arduino (as I have a few) but felt like it was overkill and Didn’t want to use 4 units or wiring that goes to each corner of the car. Also, I’ve seen so many on eBay for like $5 I figured there has to be a cheap IC approach.To create a sweeping indicator (Audi-indicator), I decided to get a 555 timer to generate my about 0.07sec per light flash rate using a 8.2kand 1kresister (I think). Flash rate is all good. I found this from roughly 85 flashes a minute and running 10 lights.Now, I was considering to use a LM3914 in bar graph mode to allow me to have a signal at around the wanted timing. From here as my led-chips are almost a watt each, I was gonna use a mofset or something similar. Somehow, I can’t seem to get the signal from the 555 timer to work with my 3914. Any ideas?Happy to completely scrap this and use someone’s design if they have one?Any idea how Audi themselves do it?Is there perhaps a dedicated chip that does this already?Please ask questions or just tell me how you’d do it as I may have done a silly billymistake.Thanks on advance. Happy to be part of the team.

author: jbeng
author_rank: Regular Contributor
timestamp: December 05, 2019, 05:07:35 am
content: Does the LM3914 portion of the circuit function properly as a bar-graph meter so far?If so, the first thing you'll probably want to do is slow your 555 oscillator frequency (probably by a factor of 10). Then, connect the input of the LM3914 to pin 2 of your 555. The signal at that point in the 555 circuit is the voltage on the capacitor, which is pretty much a sawtooth waveform. That is what you want; the output pulse from the oscillator (pin 3) won't work in this application.

author: NOKA
author_rank: Newbie
timestamp: December 05, 2019, 07:58:04 am
content: Thank you for your advice.If I may ask though, why pin 2 on the 555 timer? I have pulled out my breadboard to have a look and have noticed it’s a different signal. So I used “random” resistors I had flying around to get a reasonable flash rate. (Maybe twice a second output pin 2)Now, the lm3914 isn’t doing what I’d like it to. I have hooked up pin 1 to led 1 and pins 10-18 as well.Pin 2 and 4 to gnd and pin 3 to V+. Also hooked up pin 9 to pin 3 to get it to trigger bar graph and I have nothing. None of the led’s come on. Either there’s not enough power behind it as I’m only operating on around 3.3v.. or I’ve done something wrong again. Even the output from pin 3 of the 555 timer as input for pin 5 (lm3914) isn’t doing anything. I’ll attach a drawing of what I have doneEdit:Just realised I have drawn pin 2 and 3 on the diagram wrong. Pin 2 is ground. Pin 3 is V+. Pin 4 ground.

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 05, 2019, 10:36:27 am
content: An LM3914 will take a voltage as input and light the corresponding amount of LEDs.For your application it should be fed a sawtooth waveform.Just google 555 sawtooth.Why not use something like a WS2812b LED strip?

author: jbeng
author_rank: Regular Contributor
timestamp: December 05, 2019, 12:46:50 pm
content: The signal at pin 2 of the oscillator is a sawtooth waveform (with a DC offset), which would drive a bar-graph in the sweeping pattern you desire.One thing I did notice on your circuit diagram are the LEDs... if they are actually connected to the 3914 in that polarity, they will never light. The 3914 has open collector outputs, which means they are currentsinks, not currentsources. The LED anodes should be connected to V+ with cathodes to their respective 3914 output pins. When the 3914 is properly configured, no current limiting resistors on the LEDs are required; a single resistor on the "Ref Out" pin of the 3914 takes care of that.

author: NOKA
author_rank: Newbie
timestamp: December 08, 2019, 11:10:26 am
content: Quote from: jeroen79 on December 05, 2019, 10:36:27 amI honestly didn’t know they existed and I probably would have considered them but the project I am working on, individual LED’s seem to be more applicable. Thank you! This light stop will come in handy in the future!

author: NOKA
author_rank: Newbie
timestamp: December 08, 2019, 11:15:04 am
content: Quote from: jbeng on December 05, 2019, 12:46:50 pmI had to look into it a bit further and it seems to finally make a bit more sense. Will play around with the pin 2 output and will try to get my LM3914 running again. Just short on time these days.As for the diagram! I did it very quickly and yeah! The more you look at it the more mistakes come up!the leds (although wrong on drawing) are connected the right way. I’ve just done something that prohibits them to work like they should. Probably an issue in pin 6-8. Not sure yetMaybe I just need to play with the right resistor for the ref out. HmmThank you for your help! I appreciate it. I’ll keep working on it and keep an update here

author: jbeng
author_rank: Regular Contributor
timestamp: December 09, 2019, 02:17:44 am
content: I did a quick web search and saw this page on SparkFun (link below) which might give you some help in getting your display circuit running when you get back to it. They describe the chip operating theory and have a couple of sample circuit diagrams that look pretty good.https://learn.sparkfun.com/tutorials/dotbar-display-driver-hookup-guide/all