anyone need POGO cable for HP 20b/30b, HP 15C LE?

[ijabbott]

Make sure the USB-to-TTL serial converter is set for 3.3V TTL and not 5V TTL. Sometimes there is a slide switch or a jumper to change the signal voltage between 3.3V and 5V.

• Pin 1 of the USB socket (VCC +5V, usually a red wire) not connected.
• Pin 2 of the USB socket (D- signal, usually a green wire) goes to TXD on the USB-to-TTL-3.3V serial converter.
• Pin 3 of the USB socket (D+ signal, usually a white wire) goes to RXD on the USB-to-TTL-3.3V serial converter.
• Pin 4 of the USB socket (GND signal, usually a black wire) goes to GND on the USB-to-TTL-3.3V serial converter,
  

Some people recommend the use of a 1KΩ resistor on the TXD signal, at least for the HP 20b/30b because they are expecting 3V signal levels, not 3,3V, and the resistor mitigates for the slight over-voltage.

You don't have to use PL2303 modules. FT232R or CH341A modules should do as well, as long as they are TTL 3.3V (sometimes written TTL 3V3).