I have been able to do this previously with a 5v Pro Mini, by simply connecting pins 11-13 (MOSI, MISO, and SCLK), Vcc, and GND on the Uno to the same pins on the Pro Mini, and pin 10 on the Uno to Reset on the Pro Mini. After loading the 'Arduino as ISP' sketch to my Uno, I can then load my required sketch via the Uno to the Pro Mini. All good (most of the time...). I know there is also another method - based on removing the actual ATMEGA chip from the Uno, but that relies on you having a removable chip - which unfortunately, mine doesn't.
The problem comes when the cheapskate author inadvertently buys a bunch of 3.3v Pro Minis in error - thinking "Wow, these are really cheap!!"
I have read various contradicting reports about programming them, saying things like
My understanding is that the 3.3v Pro Mini boards are designed simply to allow easier interfacing with 3.3v sensors and peripherals - the board itself is the same with the exception of the on board regulator, and oscillator/crystal. So it seems to me that the argument about both 5v and 3.3v Pro Minis using the same ATMEGA328P chip is valid - the only difference being that the operating voltage affects the clock speed (hence why 3.3v Pro Minis are only clocked at 8MHz). That being the case - my thinking is that to program the 3.3v version, I should be safe passing it 5v logic levels during programming, as long as the 5v Vcc from the Uno is connected to the RAW voltage input of the Pro Mini, rather than Vcc, and I select the 3.3v 8MHz board in the IDE. At least, that's my theory...
I would be keen to hear from anyone else that has actual experience programming 3.3v Pro Minis - specifically using the 'Arduino as ISP' method, and has already worked through this issue.
I don't have the time nor money to buy replacement 5v versions of the Pro Minis, nor do I really want to go down the route of having to purchase additional modules/cables etc., unless this mechanism is debunked as absolutely 100% unsuitable for use on 3.3v Pro Minis... These units will be programmed once, and then left to their own devices - so I really don't want to buy kit to program them that will be used once and then left in a drawer, if I can do it using a few dupont cables and an Uno.
Thanks for any advice...
The problem comes when the cheapskate author inadvertently buys a bunch of 3.3v Pro Minis in error - thinking "Wow, these are really cheap!!"
I have read various contradicting reports about programming them, saying things like
- the 3.3v Pro Mini doesn't mind having the data pins overdriven to 5v - and - the absolute max logic high voltage is Vcc + 0.5v (i.e. 3.8v)
- the 3.3v Pro Mini can be programmed at 5v as long as the Vcc from the Arduino is not connected - and - the 3.3v Pro Mini needs the voltage regulator disconnected so that it can be programmed with 5v Vcc
- the 3.3v Pro Mini must use logic level shifters for programming from 5v Uno - and - both 5v and 3.3v Pro Minis use the same chip so (as long as all 3.3v peripherals are disconnected) it makes no difference!
My understanding is that the 3.3v Pro Mini boards are designed simply to allow easier interfacing with 3.3v sensors and peripherals - the board itself is the same with the exception of the on board regulator, and oscillator/crystal. So it seems to me that the argument about both 5v and 3.3v Pro Minis using the same ATMEGA328P chip is valid - the only difference being that the operating voltage affects the clock speed (hence why 3.3v Pro Minis are only clocked at 8MHz). That being the case - my thinking is that to program the 3.3v version, I should be safe passing it 5v logic levels during programming, as long as the 5v Vcc from the Uno is connected to the RAW voltage input of the Pro Mini, rather than Vcc, and I select the 3.3v 8MHz board in the IDE. At least, that's my theory...
I would be keen to hear from anyone else that has actual experience programming 3.3v Pro Minis - specifically using the 'Arduino as ISP' method, and has already worked through this issue.
I don't have the time nor money to buy replacement 5v versions of the Pro Minis, nor do I really want to go down the route of having to purchase additional modules/cables etc., unless this mechanism is debunked as absolutely 100% unsuitable for use on 3.3v Pro Minis... These units will be programmed once, and then left to their own devices - so I really don't want to buy kit to program them that will be used once and then left in a drawer, if I can do it using a few dupont cables and an Uno.
Thanks for any advice...