Finding cheap ADC - Page 1
Forum section: electronics / projects

author: nemesis_567
author_rank: Contributor
timestamp: January 22, 2022, 03:21:08 pm
content: So I'm looking for a cheap 8 channel ADC for my project and I just can't find anything sub $1.What's weird is that I can find an MCU like the ATTINY404 or 88 for sub $1 that contains an 8 channel ADC.I'm new to this, so am I missing something obvious?Thank you!

author: fcb
author_rank: Super Contributor
timestamp: January 22, 2022, 04:27:09 pm
content: More data required such as:Sample rate?Resolution?Simultaneous sampling?

author: nemesis_567
author_rank: Contributor
timestamp: January 22, 2022, 04:38:02 pm
content: Basically it's used to convert sensor data to digital, data is collected every few seconds.It doesn't need simultaneous sampling, it can sample each channel separately.8 bit resolution is enough.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 22, 2022, 04:47:13 pm
content: Supply and demand, there's not much demand for such low end ADCs apart from the ones built into microcontrollers.

author: BigBoss
author_rank: Regular Contributor
timestamp: January 22, 2022, 05:15:07 pm
content: https://www.ti.com/store/ti/en/p/product/?p=ADC081C021CIMM/NOPB&keyMatch=ADC081C021CIMM

author: Zero999
author_rank: Super Contributor
timestamp: January 22, 2022, 05:19:10 pm
content: Quote from: nemesis_567 on January 22, 2022, 04:38:02 pmIt appears you've answered your own question: use a cheap MCU and a few lines of code. Most MCUs also have a built-in analogue multiplexer, which enables one ADC to be used for multiple channels.Quote from: nemesis_567 on January 22, 2022, 03:21:08 pm

author: Siwastaja
author_rank: Super Contributor
timestamp: January 22, 2022, 05:21:40 pm
content: What's the reason for not using the MCU's internal ADC? I guess you have an MCU there anyway, how else you would interface with the ADC you are looking for?

author: nemesis_567
author_rank: Contributor
timestamp: January 22, 2022, 05:25:36 pm
content: Quote from: Siwastaja on January 22, 2022, 05:21:40 pmI2C/SPI. I don't have an MCU.It seems that using an MCU may be a more reasonable option after all. It's very weird since generally a dedicated IC is cheaper..I think I'll use ATTINY404-SSNR since I have a couple of them and it has a 10 channel ADC, more than what I need. The alternatives I can find are 3-4x times as expensive with 8 channels.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 22, 2022, 05:42:26 pm
content: So what will the I2C or SPI connect to? Some DAQ system which doesn't have analog channels?You need to make sure whatever speaks I2C or SPI, supports the ADC you are going to use. With a microcontroller, you can of course create any I2C/SPI protocol you need.Generally, dedicated ICs are more expensive than the integrated or application-specific solutions when the integrated solution is suitable to do most of the jobs. This is simply due to economics of scale; everybody buys the integrated solutions and only few need the more basic building blocks, making them more expensive. Similarly, building a car out of car parts ends up pretty expensive.I remember being amazed at the difference of a 16-bit tens of MSPS ADC costing just a few $ when it also included CCD readout control logic, when the bare ADC with similar analog performance but without the CCD control logic costed like $100. Same can be seen in battery management IC's, one with many ADC channels, level shifters, current sense amplifiers is cheaper than any of those subparts bought separately; simply because battery management ICs sell in gazillions.

author: nemesis_567
author_rank: Contributor
timestamp: January 22, 2022, 05:47:08 pm
content: Quote from: Siwastaja on January 22, 2022, 05:42:26 pmYes, it connects to an RPI. I have no analog inputs.Quote from: Siwastaja on January 22, 2022, 05:42:26 pmI was using an MCP3008 but it is ridiculously expensive, at least over here in comparison to these full-fledged micros. I suppose flashing a micro is takes less than a minute so it shouldn't justify the extra cost.

author: fcb
author_rank: Super Contributor
timestamp: January 22, 2022, 06:36:31 pm
content: Use a single channel ADC (e.g. MCP3021) with a cheap multiplexor on the front (CD4051B/HEF4051), drive this with 3 i/o if you are using a Pi.As you have 5V(?) then a MAX11064 is xs Digikey. Also the MCP3208 is xs LCSC.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: January 22, 2022, 06:39:37 pm
content: Quote from: nemesis_567 on January 22, 2022, 05:25:36 pmI design low cost USB scopes and either use a PIC32MX series with internal A2D or use the PIC with an external AD9201 which can sample up to about 20 Mega samples/sSounds like a simple PIC would do the job maybe even a low cost PIC16F series ?

author: nemesis_567
author_rank: Contributor
timestamp: January 22, 2022, 07:19:49 pm
content: Well at 55 cents the Attiny404 still beats it.

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2022, 10:07:25 pm
content: Quote from: nemesis_567 on January 22, 2022, 05:25:36 pmLOL what? The exact opposite is the case. Tons and tons of dedicated ICs have been discontinued because it's cheaper to do in a cheap MCU. Obviously not in every instance, especially in analog stuff where the magic is in the specialized analog circuits.

author: nemesis_567
author_rank: Contributor
timestamp: January 22, 2022, 10:11:19 pm
content: As a newbie in the subject it seemed counter-intuitive to me that it would happen, otherwise why bother making dedicated chips if the blunter tool could solve that and many other problems at once. But I forget that historical reasons may have justified, and if not play an important role like you just described. It somewhat makes sense now.

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2022, 11:16:07 pm
content: The sheer volumes that MCUs can be made in, thanks to them being blank slates so to speak, allows for lower costs than a very specific low-volume IC would be.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 23, 2022, 07:20:44 am
content: Use a padauk mcu, it's cheap and has internal ADC, something like PFS173-S08

author: Siwastaja
author_rank: Super Contributor
timestamp: January 23, 2022, 07:37:51 am
content: Quote from: nemesis_567 on January 22, 2022, 10:11:19 pmDedicated "subparts" such as ADCs are always needed in large enough quantities justifying making them.Still, more integrated "application solutions" are needed in even larger numbers, meaning two mechanisms for lower price: large volume, and more competition.It's worth understanding that the silicon itself costs nothing. The price is mostly defined by 1) NRE costs dominating with very low volumes, 2) basic market equations regarding supply and demand dominating with medium to high volumes. Also remember that the distributors like Digikey do not use any constant markup mechanisms, supply and demand is also at play. When youneedsomething and don't have many choices, higher profit can be asked. You are going to buy a few thousand max anyway; if you were making a large scale product, you would be buying those more integrated parts and price would be possibly #1 competition argument.

author: nemesis_567
author_rank: Contributor
timestamp: January 23, 2022, 10:04:21 am
content: Quote from: ali_asadzadeh on January 23, 2022, 07:20:44 amThere's the added cost of the programmer + emulator, so it's no longer very appealing.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 23, 2022, 02:57:30 pm
content: QuoteThere is a thread in EEVblog that makes an opensource and cheap Programmer based on STM32F072 part.