Hi gang, I'm having a hard time programming my Arduino Pro Mini 3.3V 8MHz microcontroller. I've spent a couple days now with the help of Google's Gemini AI but I continually get a timing error as I initiate the code dump. I'm thinking now that I just might have a Pro Mini 5V device in front of me (?) My question, before we get into all the "did you setup your Arduino IDE device & ports properly" and "did you set your SparkFun USB to Serial adapter to the proper 3.3V setting" .... I simply want to know if a Pro Mini can be visually identified on the bench? Specifically Gemini suggests that I can apply the positive terminal of a 9V battery to the "RAW" pin and the negative terminal of the battery to the "GND" pin. If I measure +3.3Vdc out on the regulated "VCC" pin then that proves you have a Pro Mini 3.3 8MHz. However, I also read that a 3.3V Pro mini can be setup/modified to output +5V on that same "VCC" pin ....assuming that the RAW is greater than 9V. My test is showing a regulated 5Vdc out on "VCC"......Please help.
If you are getting 5V output from the regulator then its running at 5V. Is the regulator marked LB/KB33 or LB/KB50? Are you sure that the resonator/crystal is 8MHz?
Maybe, there are many clones around and a 3.3v Pro-mini can work on 5v just as well.
A 3.3v should come with an 8MHz resonator vs a 16MHz resonator for the 5v version
There should also be a difference in the onboard regulator. If the RAW pin is powered with 9v and GND, then the Vcc pin should be 3.3v to GND.
On the 5v versions i have the regulator shows LG50 and i can't read what is on the 3.3v regulator.
As i said the difference is in the resonator,
Simplest solution is to power it using 5v on the Vcc pin (and GND to GND) and try and upload a simple sketch at 5v logic levels, using first 16MHz as a clock speed and then 8MHz as a clock speed, and either one of them should work properly.
If you need a 3.3v Pro-mini specifically because you want to use it at lower voltages and it turns out there is a 16MHz resonator on the board, you may be able to use MiniCore to just program it as a barebones 328P and set the fuses for an internal 8MHz (or less)
You can also try and read the fuses, You can do that using SPI. But be careful, a High Voltage programmer for a 328P is a lot of work.
I just returned 3 Pro Mini's to Amazon so I can't say for sure. The two other Pro Mini's I have in stock at home (which all respond the same when programming) are an Arduino and a Deek-Robot. The Deek-Robot is marked "LG50" and it's crystal simply says "AR". The Arduino's regulator is stamped "S8Xt" and it's crystal is "80". Are you saying if I measure 5.0V out on the VCC pin (while applying 9Vdc on the RAW) then my Pro Mini is in fact a 5V 16MHz device? I absolutely require a 3.3V 8MHz Pro Mini as this little hand-held remote project I'm designing will operate off a LiPo battery .... with nRF24L01 radio.
Maybe buy the real SparkFun one? You have a far better chance to get what you want; but it comes at a price.
Well the LG50 is a 5V LDO, so the Deek Robot is a 5V device, which the resource here appears to confirm.
I wasn't able to find anything for S8Xt or the crystal markings. An 8MHz crystal might be marked '8.000', '80'0', '80.0M' and I guess there may be other variants on clone boards - although I am nott making any assumptions about that here. Perhaps you could confirm? An oscilloscope would confirm the frequency for sure.
VCC is the power input to the MCU which is supplied by the regulator. If your multi-meter is measuring 5V there, then that is what is being supplied from the regulator. Whether it should be is another matter.
Typically the 3.3V boards run at 8MHz and the 5V boards at 16MHz. If the crystal on the Arduino board is running at 8MHz then that would seem to suggest a 3.3V board with a shorted regulator? The 328P is 5V tolerant, but there isn't an option under Tools in the IDE for 'ATmega328P (5V 8MHz)'. However, I would perhaps expect the 'ATmega328P (3.3V 8MHz)' option to still work as it is the clock frequency that is significant. Of course, if the regulator is damaged, then there has to be a reason and then who knows what over problems may exist.
I think that's my next move. Thanks
Not necessarily. Perform the test as i outlined try and upload blink using 8MHz as clockspeed and 16MHz as clockspeed. Only one should work.
It's a resonator not a crystal, but that may actually suggest something with an 8 something. Impressed you can read anything at all.
Even just for completions sake you should post how you have hooked up the USB to TTL bridge.
I've shared a schematic here of the Pro Mini and it clearly shows (in the top left) a fixed voltage regulator circuit driven by the RAW input voltage pin. The fixed/regulated output voltage turns on the onboard power LED. Assuming the SJ1 jumper is not cut, this regulated output voltage then drives the ATmega328 microcontroller and it is also supplied to VCC pins (that's the VCC pin on the long edge of the PCB and VCC to the 6pin serial control header). This schematic tells me conclusively now that a measured voltage of 5.0Vdc on the VCC pin (as I supply 9V to RAW) means I do NOT have an Arduino Pro Mini 3.3 8MHz. Again my design absolute requires a 3.3 device as I'm powering it with a LiPo battery and most importantly, I'm wired to a nRF24L01 radio transceiver which absolute must operate at 3.3V for it's CE, SCK, CSN, MOSI and MISO. I will report back to this thread when I get a proper SparkFun Pro Mini 3.3 and attempt a code upload again. Thanks for your help everyone.
Well, the schematic is a Sparkfun schematic, not a clone schematic. But I think you are right. A clone Pro Mini with an 8MHz resonator and a 5V LDO would be a defective product. It would be a fundamental parts mismatch in terms of what's normally supplied in the market, even if you could get it to run. So I think they just sent you the wrong thing. You ordered 3.3V 8MHz, but they sent you 5V 16MHz. Wouldn't be the first time that's happened.
If you are not returning this one to the seller, it could still be a useful Pro Mini to use on a different project where the sensors, etc., are 5V. You might just try uploading the Blink sketch to it after selecting 5V 16MHz as the Board in the IDE, and setting your UART adapter to 5V, to make sure it's working, and blinks at the right frequency.
The LiPo will provide something between 4.2v & 3.7v not 3.3v
From the nRF24L01 datasheet the input voltage can range up to 5.25v (if Vcc exceeds 2.7v) But yes a 3.3v device should be more practical.
Update... I just received an official SparkFun Pro Mini 3.3 8MHz and it loads code from the Arduino IDE editor nicely. Lesson: avoid those third party vendors out there my friends. Thanks to all who took the time to help out.