So I am in the process to design a VU/PPM meter. A few years ago this was easy. take some LM3915's. use the dot/bar mode for PPM/VU. Then do some precision rectifier and use 2 different circuits with different time constants.
Unfortunately the LM3915 is EOL
(I recently read even the NE5534 is EOL).
The design would use Rectangle leds 2.5mm X 5mm and I would plan to use 40 of them. It will give me some resolution and a 10cm graph.
I know that using the normal LM3915 would also be tricky but using a different reference you can put them 1db apart and get a bigger scale. it is tricky but still doable.
So for now I am thinking what I can do as the LM3915 is EOL.
A solution could be to use separate comparators and a led string driven with a current source. for 40leds this means 10 quad comparators and use them in a few current strings as 30v will just hold 10leds. Then for the dot mode it will need some gates to make this happen....it's possible but it needs a lot of IC's so not a really good option.
So next plan is to see what can be done using the lm3914.
It is the lineair variant of the lm3915. Daisy chaining them to 40leds is not a problem. The only tricky part is to convert the signal from log to lin and do a PPM and VU detection on it.
So any ideas for Log/lin conversion are welcome.
There where some fantastic IC's (that 2252 etc) but they are obsolete or over the top expensive.
-Using a MCU is out of the question
-Using lm3915's sourced from ebay etc is also out of the question.
I want something build with parts that are not EOL
Unfortunately the LM3915 is EOL
(I recently read even the NE5534 is EOL).The design would use Rectangle leds 2.5mm X 5mm and I would plan to use 40 of them. It will give me some resolution and a 10cm graph.
I know that using the normal LM3915 would also be tricky but using a different reference you can put them 1db apart and get a bigger scale. it is tricky but still doable.
So for now I am thinking what I can do as the LM3915 is EOL.
A solution could be to use separate comparators and a led string driven with a current source. for 40leds this means 10 quad comparators and use them in a few current strings as 30v will just hold 10leds. Then for the dot mode it will need some gates to make this happen....it's possible but it needs a lot of IC's so not a really good option.
So next plan is to see what can be done using the lm3914.
It is the lineair variant of the lm3915. Daisy chaining them to 40leds is not a problem. The only tricky part is to convert the signal from log to lin and do a PPM and VU detection on it.
So any ideas for Log/lin conversion are welcome.
There where some fantastic IC's (that 2252 etc) but they are obsolete or over the top expensive.
-Using a MCU is out of the question
-Using lm3915's sourced from ebay etc is also out of the question.
I want something build with parts that are not EOL
This doesn't directly answer answer your question but as to the LM3915, I would have thought at this point in time you could come up with some new stock. You rule out Ebay and that's fair enough but there are lots of cheapo boards/projects using these chips for sale. Could be worth taking a chance to scavenge the chips.
Donberg list them as available for example:
Donberg list them as available for example:
Hello Thanks for the info.
That pricing seems good and thanks for the info. I am thinking about stocking them. But it's not so easy to say how much....
It did give ma an idea as they are pin compatible I could make a display PCB using the lm391x and if the lm3915 isn't available anymore in the future I only would need to change the detection circuits.
That pricing seems good and thanks for the info. I am thinking about stocking them. But it's not so easy to say how much....
It did give ma an idea as they are pin compatible I could make a display PCB using the lm391x and if the lm3915 isn't available anymore in the future I only would need to change the detection circuits.
Have a look at this project using the log RC-discharge voltage curve as reference:
https://www.eetimes.com/simple-high...-display-architecture-uses-analog-comparator/
Resolution and number of leds can be scaled as required (up to the limit of hardware).
just add a precision rectifier and a hold circuit if needed.
https://www.eetimes.com/simple-high...-display-architecture-uses-analog-comparator/
Resolution and number of leds can be scaled as required (up to the limit of hardware).
just add a precision rectifier and a hold circuit if needed.
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I am building an analog meter that has a log scale as well as a PPM scale. For the log scale, I am using a transistor to do the linear to log conversion, and for the PPM scale, I am using an opamp with transistors to do a piecewise approximation of the PPM curve. I then drive an analog meter, but you could just substitute the linear bar-dot circuit.
Here is a description of the piecewise linear approach to PPM conversion:
https://www.bbceng.info/ti/eqpt/ME12_10.pdf
and here is an excellent design that has a 100dB log converter along with precision rectifier and peak hold circuits.:
http://www.tronola.com/html/level_meter.html
Terry
Here is a description of the piecewise linear approach to PPM conversion:
https://www.bbceng.info/ti/eqpt/ME12_10.pdf
and here is an excellent design that has a 100dB log converter along with precision rectifier and peak hold circuits.:
http://www.tronola.com/html/level_meter.html
Terry