Missing resistor in a voltage divider network

[hevans1944]

LM3914.

Thanks for the link! I thought this part was obsolete, but it appears to be going strong and is recommended for new designs by Texas Instruments. The TI datasheet is comprehensive and even has a simplified schematic diagram of the flash analog-to-digital converter used in the LM3914.

...
The LM3914 is not a VU meter, it is linear.
The LM3915 is a 3dB step meter.
The LM3916 has a VU meter arrangement.
Bertus

Are the LM3915 and LM3916 still in production?

 

[bertus]

Hello,

In Holland the LM3914 and 3916 are still available:
https://www.bitsandparts.nl/LED-Dis...Dot-Bar-display-driver-(LED-VU-meter)/p113680
https://www.bitsandparts.nl/LED-Dis...Dot-Bar-display-driver-(LED-VU-meter)/p113681

In Amsterdam, they are all 3 available:
http://www.rotor.eu/indexprog.php?page=artdet.php?art=LM+3914
http://www.rotor.eu/indexprog.php?page=artdet.php?art=LM+3915
http://www.rotor.eu/indexprog.php?page=artdet.php?art=LM+3916
2 directly in the shop, 1 on internet order.

bertus

 

[hevans1944]

I would imagine that TI or National Semiconductor made a boatload of all three IC types back around the turn of the century. Now the 3915 and 3916 are still widely available here in the States from Internet sellers, such as eBay, but no more are being made to the best of my knowledge. Perhaps the Chinese will copy the chip die and begin manufacturing again if there is sufficient demand, but I would not design either IC into new equipment unless the customer bought enough spare parts to maintain that equipment over its useful lifetime. The LM3914, OTOH, appears to be viable for awhile at least. I might purchase a dozen or so to play with to see if you really can stack them up to drive 100 LED outputs!

Just in case nobody noticed, it is now easier to implement a traditional "analog" VU meter display with a color LCD dot-matrix display driven by a dedicated microprocessor. I haven't actually seen such a display up close, but similar "analog replicas" appear on high-end amateur radio gear as "S" meters to indicate received signal strength or as SWR meters to indicate forward power to reflected reverse power ratio, and I am pretty sure they also appear as "analog" VU meters on professional audio mixer boards used by recording studios. Why analog? Because audio recording professionals are comfortable watching the meter needle movements of an analog VU meter to set recording audio levels. I'm pretty sure they don't want and cannot use a digital representation. But the cost of a backlit color LCD dot-matrix display and associated microprocessor with a fast analog-to-digital converter has got to be cheaper than a quality D'Arsonval lighted meter movement and its associated analog electronics. The difference adds up quickly when you are building a mixer board with a hundred or so VU meters. There might even be a niche market for gutting a used VU meter and inserting the LCD/microprocessor to replace the D'Arsonval meter movement.

 

[hevans1944]

Hello,

In Holland the LM3914 and 3916 are still available:
https://www.bitsandparts.nl/LED-Dis...Dot-Bar-display-driver-(LED-VU-meter)/p113680
https://www.bitsandparts.nl/LED-Dis...Dot-Bar-display-driver-(LED-VU-meter)/p113681

In Amsterdam, they are all 3 available:
http://www.rotor.eu/indexprog.php?page=artdet.php?art=LM+3914
http://www.rotor.eu/indexprog.php?page=artdet.php?art=LM+3915
http://www.rotor.eu/indexprog.php?page=artdet.php?art=LM+3916
2 directly in the shop, 1 on internet order.

bertus

The Bits and Parts website has a link to the LM3916 datasheet which contains a wealth of information on how to create VU and PPM (Peak Program Meter) digital bar-graph displays using the LM3916, and how to extend the input range by cascading it with the LM3915.

Anyone who wants to do as I suggested in post #23 (design and build a LCD dot-matrix representation of an analog meter) should start by studying this original National Instruments datasheet before writing a single line of code. The audio recording industry may have gone fully digital in this century, but our ears are still logarithmic-responding analog devices AFAIK. And why would anyone want to do this? Because those spiffy LM3915 and LM3916 ICs are obsolete and are no longer manufactured by National Instruments or Texas Instruments (who absorbed NI) or anyone else that I could find. There are no suitable replacements.

I did a some more Google searching for LCD simulations of analog meters and finally found this blog entry by amateur radio operator DuWayne Schmidlkofer, KV4QB, which was linked to from this dangerous site. I also found jillions of LED projects that took the LM3914, LM3915 and LM3916 ideas to make bar-graph type audio VU meters and audio spectrum analyzers and audio color organs using Arduino and RPi microprocessors, which of course is not what I was looking for at all but are spiffy projects in their own right. Here is another post from the spark-fun website that also illustrates what I am looking for.

So, anyhoo, it appears that what I want to do as a hobbyist has already been done by at least one other ham and a few other interested parties. But I knew someone had done it, because I can buy (if I could afford it) a really nice Japanese transceiver with all sorts of color TFT LCD touch-panel bells and whistles, including a simulated analog "S" meter along with lots of other "goodies" such as a waterfall spectrum display... I could add this stuff externally to my KX3 transceiver, but it already has a bar-graph SWR and S-meter display built in. A small external waterfall spectrum display accessory is available too. Oooh! So much technology, so little time (and money) left to play with it!

 

[Bish70]

I do know this, having played with flash A-to-D converters in the 1970s. I doubt you are "potentially in the mire" because you have the ability to discover how it was done, lo! those many moons ago. And that is why no one that I know actually builds flash converters from discrete components anymore... except as an educational exercise. They already exist as integrated circuits with binary coded outputs.

At one time there was a bar-code display that was used as a VU (Volume Unit) meter in some hi-fi audio rigs. This display device consisted of ten or twelve (I forget how many) LED bars stacked one above the other that would successively illuminate and stay on as the sound level increased. The number of bars illuminated was an indication of the VU level, important for magnetic tape recording. As the sound level decreased, the number of bars illuminated also decreased. A special integrated circuit (LM3914, see post #19 below by @Harald Kapp) accepted audio input and performed a flash A-to-D conversion whose output was very much the same as the circuit you posted. The major difference was the conversion was deliberately non-linear because that's the way VU meters roll. Later, a similar IC (I think this was the LM3814 that Harald linked to in his post below) provided linear steps to light up successive LED bars. I think that one may still be in production somewhere, but I haven't bothered to research that.

There are integrated circuits that will accept binary coded inputs and produce segment-driver outputs for 7-segment displays. It is a "good thing" that you are learning about this stuff, especially if your goal is to eventually become an accomplished integrated circuit designer.

BTW, op-amps are not ideal comparators for flash converters because op-amps are too slow. The only reason that I know of to actually use a flash converter is speed of conversion. With fast comparators, they will out perform any other analog-to-digital conversion circuit I can think of. Software defined radios (SDRs) may use flash converters, as do some military sensor applications, but successive approximation conversion is cheaper and less complicated and usually "gud enuf". You should be learning about these as well as integrating-type analog-to-digital conversion.

EDIT: Thanks @Harald Kapp for finding the modern LM3914!

Hi Harold,

You clearly have a huge amount of experience and knowledge in this area, my apologies for the reply I’d sent, I was being a bit paranoid.

Thank you for the reply, it is very interesting to so how much has changed in the electronics world and it’s difficult to comprehend how far it will go.

I appreciate all the help on this thread, it helped build my knowledge and confidence in this alien world, I’m sure I’ll be back.

Neil

 

[hevans1944]

@Bish70: Always remember (at least) these two things: (1) Never stop learning and (2) Always endeavor to have FUN. Electronics is supposed to be fun. Lifelong learning is a habit with its own rewards.