LM3914 - What is used now, how flexible are they? - Page 1
Forum section: electronics / projects

author: 741
author_rank: Frequent Contributor
timestamp: September 19, 2019, 08:59:51 am
content: I'd like to make a centre-zero led dot readout, 0 to 0.6V. The LM3914 has been around a while - perhaps because of features like current output and both sides of comparator string being available. How do more recent chips compare?If I do end up using an LM3914, then is there a "known good" cheap source?(While it is probably possible to program a PIC to replicate the comparators using an A/D and perhaps brightness using PWM...I'd prefer not to get into that just now).The basic resolution of an LM3914 can be enhanced with brightness control - In this PDF (https://www.americanradiohistory.com/Archive-Electronics/Electronics-Circuit-Designers-Casebook-5.pdf), look for the phrase "display expands".

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 19, 2019, 10:37:09 am
content: The LM3914 is one of those "classic" linear bipolar devices which will always will have a loyal following for years to come.Unfortunately it has been mostly superseded in most high-volume projects by other display technologies.And even if you still want to employ discrete LED bargraphs, it is usually best to use a microcontroller and either drive it directly from its output ports, or use an I2C driver which allows many more features, like dimming, flashing and individual segment control.Some driver ICs have so many outputs that an actual RGB bargraph can be implemented.Related to sourcing; you may of course, obtain them from Ebay. Caveat emptor.The best is to obtain them from a reputable distributor, although they will cost more.

author: austfox
author_rank: Regular Contributor
timestamp: September 19, 2019, 12:45:14 pm
content: For those in Australia, Rockby have National branded LM3914s in DIP packages on their specials pages this month at 3 for $5.

author: Zero999
author_rank: Super Contributor
timestamp: September 19, 2019, 02:33:07 pm
content: An array of LM339s, some resistors and a voltage reference will give you a basic bargraph display, but not dot mode, will require more parts.Why not just use a microcontroller? It will work out much easier and cheaper. The LM3914 is dead because no one uses it in new commercial products any more. Updating ones skills to use modern components is vital for continuing to progress.

author: Yansi
author_rank: Super Contributor
timestamp: September 19, 2019, 04:12:54 pm
content: I'd like to correct a bit: The LM3914 (linear mode) is the only one of the series currently still being produced by Texas Instruments, if I am not mistaken. So probably, someone is using them somewhere.LM3915 (the log one, for audio purposes) is no longer made. But most audio equipment used chained LM339 comparators with a precision opamp rectifier in front of them - no wonder, as the pricing of the LM3915 at utmost respect is (or was) pretty nonsense.Also, the use of LM339 gave the ability to use unequal step, as the resistive network may have been designed arbitrarily.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 19, 2019, 04:22:19 pm
content: Yep. And yes I'd use an MCU for that these days. This has been discussed in another thread not long ago. (Threads about the LM3914/15 seem popular, a bit like threads about Arduino on Atmega. Looks like some kind of hardware fetish.)But yes, the LM3914 is still active at TI:http://www.ti.com/product/LM3914As to implementing that on an MCU, it will give a lot more additional possibilities. And, for those into hardware fetishes, why not mix them, and emulate an LM3914/15 in an Arduino Uno?You can consider coupling any small MCU to a CAT4016 (https://www.onsemi.com/products/power-management/led-drivers/linear-led-drivers/cat4016), for a pretty nifty and beefy solution.

author: Yansi
author_rank: Super Contributor
timestamp: September 19, 2019, 04:36:47 pm
content: The current and money consumption of a CAT4016 + MCU solution will become another not-that-much-sense.I'd rather chain a couple LM339s instead, as was well done in the past. If high enough supply voltage (15 to 30V or so) is available, one can supply a whole string from a single PNP current source.Or just drive the LEDs directly by the MCU, if its GPIOs are up to the task.(Also, interesting to note the wonder of mass production, the MBI5024 LED driver ... which I think is the equivalent of TLC59282?)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 19, 2019, 05:38:33 pm
content: Note that, most generally, it is a 10-bit unary flash ADC. Unary meaning bit position or bit count, depending on configuration of course. Having a fully differential REF input (the ends of the resistor divider), it can be used for multiplication and division operations -- very handy, if a bit light on accuracy.And as a flash ADC, it's quite fast, ~microseconds. Considering a lot of similarly priced, contemporary,  ADCs took 10-100us to convert 8-12 bits, that's really not that awful.It also has constant current outputs and a crude internal reference, neither of which would be terribly easy to replicate with just an MCU (but which can be dealt with in typical applications). And the current is set by the ref, so...If you use the output currents to drive a summing node on a transimpedance amplifier, with thermometer coding enabled, you get an implicit DAC as well, so you have a full analog mul/div section (again, if you don't mind that there's an chunky internal quantizer there).Tim