pspeth
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Add Analog to Digital pins to the pi

Fri Sep 28, 2018 3:11 pm

I didn't find anything specifically on this but I would love to see 2 or 4 Analog to Digital inputs on a future pi.
This would streamline interfacing with a huge number of existing sensors out there.

This could even be shipped without the pin headers. Keeping the basic form the same for existing products.
It could also be shipped as a 5 dollar extra version of the pi.

W. H. Heydt
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Re: Add Analog to Digital pins to the pi

Fri Sep 28, 2018 3:51 pm

Not a bad suggestion. My concerns are that the SoC may not have the needed inputs (which would, in turn mean adding the feature to future SoCs--very expensive--or adding an ADC to the board--where?), something else would have to be removed to make space for the pins, even if not populated, and the ever popular--how many people actual need this (the answer *may* be "lots"), because this would add cost for everyone when not everyone needs or wants it.

As it is, you can always add ADCs through the use of HATs or external circuitry.

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Burngate
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Re: Add Analog to Digital pins to the pi

Fri Sep 28, 2018 5:27 pm

Also, whilst "lots" of people may want ADCs, their needs vary.
Does everyone want 24-bit resolution? How about speed - 44kHz for audio, rather less for blood pressure.

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mahjongg
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Re: Add Analog to Digital pins to the pi

Fri Sep 28, 2018 5:46 pm

Or what about >3MHz speeds for Video? :roll: :shock:

In any case the current silicon process used for the SoC probably doesn't support analog circuitry (except perhaps for some switching supply logic, The previous PI's used an voltage controlled supply for the core, but probably that is done with digital logic too, just a few stronger digital transistors). Real analog logic usually means using a different fabrication process. The PI's SoC is not built using a silicon process, like an ATMega is designed with.

And speculating about a new PI is quite pointless, (except perhaps for gauging the need for something, but then one user who wants something isn't statistically relevant) everything you could want has been already thought about by the RPF, and sometimes the RPF does hold sessions where you can express your wants and needs, they are just not using this forum for that.... :mrgreen:

lbdroidman
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Re: Add Analog to Digital pins to the pi

Thu Oct 18, 2018 6:14 pm

Isn't 100% of the purpose of that big pin header along the top of the board for the purpose of adding the random stuff that YOU like?
There are two problems with the kitchen sink approach to hardware like this;
1) if you added every possible thing needed by... everyone, the cost would rise from $25 to $infinity, and that is not acceptable.
2) if you added every possible thing needed by... everyone, the size of the board would grow from [size of credit card] to [infinity], and that is not acceptable.

So if you want an ADC, you pick an ADC that meets your specific requirements, and add it yourself.

https://www.bc-robotics.com/shop/16-cha ... pberry-pi/

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Re: Add Analog to Digital pins to the pi

Fri Oct 19, 2018 9:39 am

mahjongg wrote: Or what about >3MHz speeds for Video? :roll: :shock:

In any case the current silicon process used for the SoC probably doesn't support analog circuitry (except perhaps for some switching supply logic, The previous PI's used an voltage controlled supply for the core, but probably that is done with digital logic too, just a few stronger digital transistors). Real analog logic usually means using a different fabrication process. The PI's SoC is not built using a silicon process, like an ATMega is designed with.
You *can* have analogue circuitry on 40nm LP - it's just not a purpose-designed process so everything has to be a) CMOS b) sub-optimally sized.

On the Pi chips there are analogue LDOs for supplying bits inside USB/HDMI plus most high-speed serial interfaces like USB/DSI/CSI have what's termed an Analogue Front End that behaves like a very fast current-mode op-amp.

One pitfall of a hypothetical future ADC that can be mapped on to GPIO pins is that the GPIOs really do not like having voltages >VIL and <VIH applied. Leakage current increases significantly and may even cause internal bits of the pad logic to oscillate. With prolonged exposure to "analogue" levels, the GPIO may eventually fail.
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Re: Add Analog to Digital pins to the pi

Fri Oct 19, 2018 9:47 am

Adding new stuff like this means the price increases for everyone (or profit levels decrease), even if not everyone wants to use the feature. Which we try and avoid. As others have said, it's what HAT's are for.
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Re: Add Analog to Digital pins to the pi

Fri Oct 19, 2018 9:57 am

pspeth wrote:
Fri Sep 28, 2018 3:11 pm
I didn't find anything specifically on this but I would love to see 2 or 4 Analog to Digital inputs on a future pi.
This would streamline interfacing with a huge number of existing sensors out there.

This could even be shipped without the pin headers. Keeping the basic form the same for existing products.
It could also be shipped as a 5 dollar extra version of the pi.

https://www.goodreads.com/quotes/699462 ... all-of-the
Adieu

drgeoff
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Re: Add Analog to Digital pins to the pi

Fri Oct 19, 2018 1:06 pm

Isn't that a crib of what Lincoln is reputed to have said? https://historynewsnetwork.org/article/161924

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Imperf3kt
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Re: Add Analog to Digital pins to the pi

Sun Oct 21, 2018 9:38 pm

W. H. Heydt wrote:
Fri Sep 28, 2018 3:51 pm
Not a bad suggestion. My concerns are that the SoC may not have the needed inputs (which would, in turn mean adding the feature to future SoCs--very expensive--or adding an ADC to the board--where?), something else would have to be removed to make space for the pins, even if not populated, and the ever popular--how many people actual need this (the answer *may* be "lots"), because this would add cost for everyone when not everyone needs or wants it.

As it is, you can always add ADCs through the use of HATs or external circuitry.
Going by this logic, I neither need nor want POE, yet if I want a Pi3b+, I must accept it.
Overall, it benefits more people who can afford those expensive POE routers, so it was added.
Analogue input is a commonly requested feature I see here, the request to have it on the board itself isn't as outlandish as asking for octacore CPUs with 4GB of RAM
Stop plugging your fan directly into the GPIO 5v
https://www.electronics-tutorials.ws/power/transient-suppression.html

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davidcoton
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Re: Add Analog to Digital pins to the pi

Sun Oct 21, 2018 10:44 pm

Imperf3kt wrote:
Sun Oct 21, 2018 9:38 pm
Going by this logic, I neither need nor want POE, yet if I want a Pi3b+, I must accept it.
Overall, it benefits more people who can afford those expensive POE routers, so it was added.
Analogue input is a commonly requested feature I see here, the request to have it on the board itself isn't as outlandish as asking for octacore CPUs with 4GB of RAM
Not at all. You have to accept the POE connector, but the expensive POE stuff is on a separate, optional board. Likewise (excluding the Pi0 and Pi0W) we all have to accept the GPIO connector, but no-one has to add an unwanted HAT.

As for the analogy between octacore and RAM against ADC, it breaks down rapidly. You can't put the second four cores on an add-on board. It's all or nothing in the SOC. The choice then is to buy the correct base Pi, with one, four, or maybe eight CPUs and whatever other parts are there. But ADC, DAC, POE, relays, opto-isolators, music synths, radios etc etc etc ad infinitum all work completely satisfactorily (at least in principle) on HATs. If I need eignt CPUs and 4GB, I buy the future Pi that provides them. If I want that and not an ADC, why should I pay for an ADC that could be optional?
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Imperf3kt
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Re: Add Analog to Digital pins to the pi

Mon Oct 22, 2018 2:08 am

Hmm, you're right, my analogy was pretty flimsy.
Ah well, the threads not locked yet, so it's nice to discuss some of these things occasionally.
Stop plugging your fan directly into the GPIO 5v
https://www.electronics-tutorials.ws/power/transient-suppression.html

pcmanbob
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Re: Add Analog to Digital pins to the pi

Mon Oct 22, 2018 2:56 pm

Just for the fun of it and not to upset anyone please.......

Looking at it from a different perspective if the pi came with every option on board ( ADC, DAC, POE, relays, opto-isolators, music synths, radios etc etc etc) then no one would have to learn how to use them with the pi gpio.

Everyone would just be able to go get one with what ever project they wanted, that would remove a lot of posts on here were people ask for help using all this kit, it would leave a lot of people here with nothing to do but sit and twiddle their thumbs.

Please have a though for all those people left with nothing to do but twiddle their thumbs ... :( :(

Guess I had better get my coat now......................... :D :lol:
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davidcoton
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Re: Add Analog to Digital pins to the pi

Mon Oct 22, 2018 5:31 pm

At the risk of threadlock...
...for all we know RPF are in the final testing stgers of "MegaPi", an expanded Pi with all(!) the interfaces on board. Everything anyone has ever asked for or wanted. The board measures 1m x 1m, a new Pi standard format. RPF magic has kept the cost to £35,000. Eben will be surprised if worldwide sales exceed 10....
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dave j
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Re: Add Analog to Digital pins to the pi

Mon Oct 22, 2018 6:40 pm

Just saying "add analog inputs to the Pi" is too vague to be meaningful.

What resolution? What sample rate? How much jitter of sample times is acceptable (one built into the Pi is going to be fighting other circuitry for access to the memory bus)? How many channels? How many simultaneous channels? What sort of signals are you going to want to feed it with? What voltage ranges? Do you want negative as well as positive voltages? AC or DC coupling? What about input protection?

The moment somebody has to add an extra circuit for, say, range conversions and input protection they've lost the main advantage of having a built in ADC and it's relatively little work to add an ADC that matches their needs rather than try and use one chosen as a compromise between competing requirements.

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