Full circle with ChatGPT
Caleb Carroll
Chief Information Officer @ Vivent SA | Wireless Engineering, Applied Machine Learning
Over the past few months I transitioned from using ChatGPT as a form of personal amusement to using it like a search engine. At times when I haven't been able to find information using traditional search tools like Google or DuckDuckGo, I have been turning to ChatGPT for answers. This strategy for finding answers was working quite well until a recent update caused ChatGPT to - Well, I don't quite know how to describe it other than to say that I can no longer rely on ChatGPT to provide answers.
It was some time shortly after the ChatGPT update occurred when I was looking into using a couple RP2040 microcontrollers in a home automation project. One of the things I needed to do was to use a thermistor to measure a temperature. The first step was to get some specifications for the ADC. Rather than digging through the specifications document, I did what I had started becoming accustomed to, which is to ask ChatGPT. I usually kept ChatGPT open in one of my browser tabs all day in order to access it more quickly. I asked the question "What is the input impedance of the Raspberry Pi Pico W ADC?"
ChatGPT responded "The Raspberry Pi Pico W microcontroller board features a 12-bit analog-to-digital converter (ADC) with a single-ended input. The input impedance of the Pico's ADC is not explicitly specified in the official documentation, but it can be inferred based on the schematic and the specifications of the microcontroller used in the Pico.
The Pico is based on the RP2040 microcontroller, which has an input impedance of around 1 megaohm, according to the RP2040 datasheet. This suggests that the input impedance of the Pico's ADC is likely to be similar, around 1 megaohm."
I was happy with that answer because a 1M ohm input impedance would mean that attaching the ADC to the potential divider circuit would result in a nearly perfect 50% division of the 3.3V source. I found a couple 10K ohm resistors that were very close to 10K ohm (one was exactly 10K ohm and the other was 9999 ohms) and arranged them in a potential divider circuit in order to perform a calibration. I then took empirical measurements and found exactly the voltage I expected, 1.65V. I connected the ADC to take a reading but to my surprise I found a 42.42% imbalance with respect to the source voltage. The voltage drop across one resistor was 1.4V while the other was 1.9V. I had already taken the ADC ground offset into consideration and compensated for it, so that wasn't the issue. I was working late and was tired so I decided to leave the mystery for another day.
A few days passed and I finally found some time to return to where I had left off. My initial assumption was that I had either made a stupid mistake in a calculation somewhere or the input impedance was dropping by an incredible amount while making the measurement. After verifying that I hadn't made a calculation mistake, I decided to ask ChatGPT to provide me with the specifications...
I asked "What are the Raspberry Pi Pico W ADC specifications?"
ChatGPT replied "I'm sorry, but there is no such thing as a Raspberry Pi Pico W. The Raspberry Pi Pico is a microcontroller board developed by the Raspberry Pi Foundation, but there is no version of the board called the Pico W.
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However, if you meant to ask about the Raspberry Pi Zero W, which is a single-board computer similar to the Raspberry Pi Pico, then please let me know and I'll do my best to provide you with the ADC specifications."
What??? I was incredulous but... Did I make a typo in the name? No... R-a-s-p-b-e-r-r-y P-i P-i-c-o W. "How bizarre!" I thought to myself but, I also thought "How can I have fun with this?" I typed "Explain this then: https://datasheets.raspberrypi.com/picow/pico-w-product-brief.pdf" to which ChatGPT replied "I apologize for my mistake earlier. You are correct, there is a product called the Raspberry Pi Pico W, which is a variant of the Raspberry Pi Pico that includes Wi-Fi connectivity.
The ADC specifications of the Raspberry Pi Pico W are the same as the Raspberry Pi Pico, since they both use the same RP2040 microcontroller. Here are the specifications of the ADC on the Raspberry Pi Pico W:
I hope this information is helpful. Please let me know if you have any further questions or if there is anything else I can assist you with."
Earlier today, I realized that I've now come full circle with ChatGPT and, as a result, I decided to write this article. As I said earlier, I originally used ChatGPT only as a source of personal amusement. I've asked it many ludicrous questions ranging from "How much wood can a woodchuck chuck?" to "Can you provide only well documented and verifyable benefits which can be directly attributed to Brexit?" I haven't used ChatGPT for a few days now... I guess I just haven't been in humerous mood.
By the way, in case someone wants to know what the input impedance is, it's 32K ohms but due to SAR sample-and-hold effects, it can most accurately be modelled as a 28.5K ohm resistor.