I was recently playing with some LLMs regarding a relay driver circuit. ChatGPT generated a circuit diagram for me in ASCII art style, but it contained some errors. For fun I tried to ask some others if they could identify the errors.

Here's the diagram (formatting errors were from ChatGPT):

+5V
|
|
( ) Relay Coil
|
+----->|----+
| Diode |
| |
| |
+------------+
|
|
Drain (D) of MOSFET
|
Source (S)
|
-----
GND
|
Gate (G)---[220Ω]--- GPIO (3.3V MCU)
|
[10kΩ]
|
GND

Here's what Llama 3.1 70B said:

After reviewing the diagram, I've found a few potential issues:

- The diode is not connected to the relay coil in a way that would prevent back-EMF from damaging the MOSFET. Typically, the diode is connected in parallel with the relay coil, with the anode connected to the positive terminal of the coil and the cathode connected to the negative terminal. In this diagram, the diode appears to be connected in series with the relay coil, which is not correct.

- The MOSFET is not properly biased. The gate of the MOSFET is connected to the GPIO pin through a 220Ω resistor, but there is no pull-down resistor to ensure the gate is at a known state when the GPIO pin is not driving it. The 10kΩ resistor connected to GND is likely intended to be a pull-down resistor, but it's not clear if it's connected to the gate or not.

- The relay coil is not specified, but it's likely that it requires a higher current than the MOSFET can handle. Typically, a relay driver circuit would include a current-limiting resistor or a transistor to handle the high current required by the relay coil.

So it correctly identified one of the main issues, the flyback diode is wrong, but failed to correctly identify the issue with the MOSFET gate being directly tied to ground. I admit, it's not a typical way to draw things so fair enough, after all it did mention there was something fishy with the pull-down.

Claude 3 Haiku provided a very similar answer. It was a bit more explicit and included more details. For instance it thought there might be an issue driving the MOSFET from 3.3V, though failed to suggest a logic-level MOSFET, instead suggesting a level-shifter. It also suggested the 220 Ohm gate resistor might not be enough to protect the microcontroller. Though it also tried to correct the diagram but failed: it changed the diode to ->|<-, and didn't put it in parallel with the coil.

All in all, somewhat impressed.

However they get easily confused. I tried to improve the diagram, and asked again. Here's the updated diagram:

+5V
|
|
|
+----->|--------+
| Diode |
| |
( ) Relay Coil |
| |
+---------------+
|
|
Drain (D) of MOSFET
|
|]- Gate (G)-----+-[220Ω]--- GPIO (3.3V MCU)
| |
| [10kΩ]
Source (S) |
| |
+----------------+
|
-----
GND

And Llama 3.1 now says:

After examining the diagram, I notice a few potential issues:

- The diode is not connected to the relay coil in a way that would prevent back-EMF damage to the MOSFET. Typically, a flyback diode is connected in parallel with the relay coil, with the anode connected to the coil's positive terminal and the cathode connected to the coil's negative terminal. In this diagram, the diode appears to be connected in series with the relay coil, which is not correct.
- The MOSFET's source (S) is not connected to GND. In a typical relay driver circuit, the source of the MOSFET is connected to GND to provide a return path for the current.
- The 10kΩ resistor is not connected to anything. It's possible that it's intended to be a pull-down resistor for the MOSFET's gate, but it's not clear where it's supposed to be connected.

So it totally fails to "see" that the 10k is now correctly connected to ground, and that it shares the ground point (in the diagram) with the source of the MOSFET. At least it figures it's meant to be a pull-down.

However it did notice the diode is now correctly placed in parallel with the coil, and did again correctly see the diode was the wrong way around. So that's something.

edit: I changed the diode direction and asked if that fixed it. Llama 3.1 did not "see" that and suggested a change.

Claude 3 did much better and noticed the direction change and was happy.

As I said, was just fooling around with this and thought I'd share. They're confident, but sometimes oh-so-wrong. Still, using a service where you can ask the same question to multiple models is nice. That way it can be easier to see when they're confabulating.