DTR Capacitor value for USB-TTL Adaptor PL2303

Hi Guys

To program some ProMinis I have I always used to use the 5v, Gnd, Tx, Rx and RST pins on a UNO board, but my UNO is tied up in some other project at the moment so I'm going to use a PL2303 based USB-TTL adapter I had lying around.

Now, I know it doesn't supply a reset pulse so I'm going to modify it by adding a capacitor to pin 2 (DTR_N) of the PL3203 chip and use that to supply my reset pulse. The only problem I have is that I don't know what value of capacitor I'll need. Looking around, I see values of 47nF being quoted, but the nearest value to that I have to hand is 10nF. My next nearest is 470nF. Will the 10nF be ok to use?

I would just "suck it and see" but bearing in mind how small the joints are going to be, I only want to attempt this once!

Thanks.

The Pro Mini already includes the correct 100 nF capacitor on the DTR line. :roll_eyes:

So, to clarify for a thickhead like me, are you saying I can just bring a straight connection out from the DTR pin on the PL2303 direct to the DTR connection on the Promini to send the Reset pulse??

I was persuaded by these links by the way:

47nF value cap:
Adding-Auto-Reset-Pin-to-PL2303-based-Serial-USB-Modules

100nF cap:
Forum Link

STDummy:
So, to clarify for a thickhead like me, are you saying I can just bring a straight connection out from the DTR pin on the PL2303 direct to the DTR connection on the Pro mini to send the Reset pulse??

The Pro Mini is specifically designed to plug directly to a certain older FTDI module. So it - the Pro Mini - has the capacitor on the board. You can use any USB interface module that has the RTS or DTR brought out but need to match the arrangement of connections.

STDummy:
I was persuaded by these links by the way:
47nF value cap:
Adding-Auto-Reset-Pin-to-PL2303-based-Serial-USB-Modules

Link corrected: Adding Auto Reset Pin to PL2303 based Serial USB Modules

Ahem: The article to which you link is an "instructables"! :roll_eyes:

STDummy:
100nF cap:
Forum Link

And this article refers to "breadboarding" an ATmega chip, not a proper, complete board such as the Pro Mini. :astonished:

Nah, I'm giving up with the PL2303 junk :angry: .

I first modded the adapter by removing the existing 5way pin connector and replaced it with a 6way connector. I then soldered a lead from pin two on the chip to the extra pin, connected it up, with the new connection attached to DTR (Grn) on the Promini and hit upload to load the blink program. Nothing but the usual out of sync message. Double and triple checked I'd soldered to the correct pin and there were no solder bridges.

Flipped the Rx and Tx connections, just in case - no change. Even disconnected the new RESET lead and tried the "well timed press of the reset button" method - still the same so I've binned it.

Just have to wait for the CH430G adapter thats in the post to arrive instead. Failing that, maybe buy a spare UNO just to keep for programming the prominis.

Thanks anyway for the advice Paul__B