SPI and LM3914 possible?

Just throwing some ideas around. SPI is great but it has one disadvantage, separate CS line for every peripheral used. So I was thinking, LM3914 has dot mode when it goes low just on 1 pin depending on input analog signal level https://www.ti.com/lit/ds/symlink/lm3914.pdf So theoretically it is possible to have CS line controlled by analog output, 1 pin for up to 10 peripherals. What’s not clear how is it going to cope with PWM?

Suggest a 3 to 8 or 4 to 16 decoder.

Yes, it is a good way of saving on pins but I’d like to explore 1 to 10+ option since LM3914 can be cascaded

Interesting idea. Traditional multiplexing can be cascaded in a way also, but never mind, you wanna forge a new path.

But what means your question? Your scheme will have no advantage or disadvantage, PWM or not

or

I’d like to see the code doing the PWM on whatever you are up to and have a look about this no problem you are worried about.

a7

A PCF8574 Remote 8-Bit I/O Expander would likely be more consistent .....

I happen to have spare LM3914 and a nano somewhere, so might just mock something up quickly to see if it holds

I wonder what the delay time would be for being sure, really absolutly sure, that the voltage wanted from the PWM was stable, and thus selecting the correct SPI device ?

Funny how that works. :wink:

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OIC. That might indeed be a deal breaking.

There must be something else you can do with that LM3914. That chip was quite nice to have, I think it took up an entire chapter’s worth of application ideas.

Nothing about SPI tho. :expressionless:

Even if you got it to work, it would be fragile compared to just staying digital and using traditional approaches.

a7

I think it is, looks like low pass filter adds unacceptable delay that causes all outputs fire in sequence until the correct voltage pin is settled

Haha, I solved it: you just have to add a real DAC to your circuit.

Maybe you have one of those around that you could use.

If you do order some, get some multiplexer chips at the same time for when the original scheme just isn’t what you hoped it would be. :expressionless:

a7

Yes MKR boards have 1 DAC I guess this would work fine