LM3914 LED bar driver - Page 1
Forum section: electronics / beginners

author: NHSA
author_rank: Regular Contributor
timestamp: July 07, 2021, 05:15:00 pm
content: Hi,After getting my amplifier / fullwaverectifier circuit more or less runninghttps://www.eevblog.com/forum/beginners/problem-with-full-wave-rectifier-using-tlp082/I now added a LM3914 and a 10 LED bar in order to signalize the vibration.Now I have searched everyhwere for a LM3914 calculator in order to calculate the R1 and R2 resistor. Found this onehttps://www.electro-tech-online.com/tools/LM3914V2.phpbut what I practical see to the theory of the calculator does not fit ...Taking the formula from the TI datasheet " Ref Out V = 1.25*(1+(R2/R1)) is a bit better but only when supplying a voltage below 12 V. As I want to drive my amplifier/full wave rectifier circuit as well as the LM3914 LED bar driver with 18 Volt evrything look different. The formula from TI does not take into consideration the supply voltage while the calculator does.Anybody knows of a better calculator or is this a Trial & Error exerciseThanks in advanceregards Rainer

author: StillTrying
author_rank: Super Contributor
timestamp: July 07, 2021, 06:04:55 pm
content: The V+ supply doesn't come into it.You have to decide on the LEDs current first which gives you the value of R1.Then you can work out R2, which raises the whole 1.25V Ref up to the voltage you want for RHI.What RLO and RHI voltages do you want.Page 9 on the data sheet.https://www.ti.com/product/LM3914

author: David Hess
author_rank: Super Contributor
timestamp: July 07, 2021, 07:35:14 pm
content: Like StillTrying writes, the LM3914 datasheet has everything required and the calculations are simple and reliable.

author: NHSA
author_rank: Regular Contributor
timestamp: July 08, 2021, 12:38:25 am
content: Hi,Thanks bothRainer

author: NHSA
author_rank: Regular Contributor
timestamp: July 11, 2021, 09:29:47 pm
content: Hi,Still trying to get a result when driving the LM3914 with 18V.The circuit depicted in this messagehttps://www.eevblog.com/forum/beginners/problem-with-full-wave-rectifier-using-tlp082/is powered with +- 9V and GND for the operational amplifiers TL082.Now the problem is with the LM3914 which allegedly works up to 18 volt but when I connect it to the 18V power supply I do not get any signal. All Leds are lit up.Powering it with half the voltage e.g. +9V and the middle ground it works trouble free.I am using a 3K3 for the LED current (pins 7 toand a variable potentiometer 10K for adjusting the voltage (pin 8 to GND) which works OK for adjusting the sensitivity.Still trying to find out why it does not work with 18V.

author: Benta
author_rank: Super Contributor
timestamp: July 11, 2021, 10:44:34 pm
content: From the references to other threads, you're NOT connecting the LM3914 to +18 V, but to +/- 9 V. That's not the same. As you've seen for yourself, it works when connected to 0 and +9 V, which is exactly as it should be.

author: StillTrying
author_rank: Super Contributor
timestamp: July 11, 2021, 11:00:41 pm
content: What Benta said.If you're connecting the LM3914's GNDs to -9V, the SIG input would now appear to be at +9V to the LM3914, so all LEDs on.If in bar mode 18V would also give a dissipation problem when nearly all the LEDs are on.Is there a good reason why it can't be powered from the 0V and +9V.

author: NHSA
author_rank: Regular Contributor
timestamp: July 12, 2021, 12:27:19 am
content: Quote from: Benta on July 11, 2021, 10:44:34 pmHi Benta,Did not think about that. Another lesson learned.ThanksRainer

author: NHSA
author_rank: Regular Contributor
timestamp: July 12, 2021, 12:33:57 am
content: Quote from: StillTrying on July 11, 2021, 11:00:41 pmHi,Well my reasoning is that one battery will drain sooner then the other ¿ or ?My thinking was to go down from 18V (2X 9V square battery) to a 12 V power brick and after reading Benta's answer there is then the same problem.Interesting Stuff.Thanks Rainer

author: StillTrying
author_rank: Super Contributor
timestamp: July 12, 2021, 01:14:47 am
content: Quote from: NHSA on July 12, 2021, 12:33:57 amYes, but running the LM3914 off +/- 9V wouldn't save any of the current from the +9V at all, at least with the -9V now being little used not lighting the LEDs you could swap the +9V and -9V batteries half way though their life.And the LM3914 should run cooler having to drop only 7V on the LED outputs rather than 16V.I've got a few rechargeable full voltage PP3s 8.3V to 9.8V, the lower voltage down to 7.2V versions probably have higher mA hours and would do for your TL op amps.

author: Old Printer
author_rank: Frequent Contributor
timestamp: July 12, 2021, 12:54:00 pm
content: I recently had a project where the LM3914 looked like a good candidate, I was making a VU meter for a small audio amplifier. I was disappointed to find that the DIP packaged version had been discontinued and it was SMD only from the large vendors, DigiKey Mouser etc. That put me in the realm of suppliers on ebay and the like where i am always wary of counterfeit chips. Were you able to find a reliable source for good DIP packaged chips, or did you use the SMD versions?

author: David Hess
author_rank: Super Contributor
timestamp: July 12, 2021, 02:23:11 pm
content: Quote from: Old Printer on July 12, 2021, 12:54:00 pmEven worse TI now only produces it in the 20 pin PLCC package. Was there no SO (small outline) package they could have used?

author: Zero999
author_rank: Super Contributor
timestamp: July 12, 2021, 02:44:27 pm
content: I don't think I would bother with LM3914. Nowadays, I'd use an MCU, or if I really had to go analogue: 3 quad op-amps/comparators, a cheap reference, such a TL431 and a butt-load of resistors.

author: NHSA
author_rank: Regular Contributor
timestamp: July 12, 2021, 05:03:18 pm
content: Quote from: Old Printer on July 12, 2021, 12:54:00 pmHi,I have some here so I do not plan to buy them new right now.regards Rainer

author: NHSA
author_rank: Regular Contributor
timestamp: July 12, 2021, 05:08:34 pm
content: Quote from: Zero999 on July 12, 2021, 02:44:27 pmHi,I still have some LM3914 laying around so it was logical that I wanted to use them.Using op amp instead of LM3914 means 1 op amp for every Led and so I would need 10 additional op amps for my 10 LED bar. Lots of resistors and lots of space. Anyhow interesting idea for a future project.May I ask which MCU ¿?Thanks Rainer

author: Zero999
author_rank: Super Contributor
timestamp: July 12, 2021, 09:51:03 pm
content: Quote from: NHSA on July 12, 2021, 05:08:34 pmThe TL084 & LM324 have 4 op-amps, so 3 ICs would give 12 op-amps, 10 of which can be used as comparators, with the remaining two as op-amps for the rectifier. They're much cheaper than the LM3914.QuoteAny MCU with an ADC input and at least 10 output pins for the LEDs. Here's a link to a bargraph meter with 20 LEDs, using the PIC16F686.http://www.electronics-lab.com/project/bargraph-voltmeter-0-5v-dc-range-pic16f686/

author: NHSA
author_rank: Regular Contributor
timestamp: July 12, 2021, 11:54:38 pm
content: Quote from: Zero999 on July 12, 2021, 09:51:03 pmHi Zero999,Thanks. I will think about the opamp solution which is somthing new, but now ¿ where is the fun by buying ready made stuff ?As I mentioned earlier it is also a question of the size of the ready made enchilada.Thanks again and regardsRainer

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2021, 08:08:26 am
content: Quote from: NHSA on July 12, 2021, 11:54:38 pmWho said anything about ready made stuff? Check out the link I posted again. It's someone's bargraph display project. It looks like it's bought off the shelf, because they got the PCB made professionally. I consider using an MCU more of a challange in this case. Where's the fun in taking an IC, copying the schematic off the data sheet and soldering it to a board?