Just to close this out: I ordered the Adafruit FTDI friend and connected with no problems: https://www.adafruit.com/product/284?gclid=EAIaIQobChMIpoDylsSr7AIVwT2tBh2qDwBwEAQYASABEgISlvD_BwE And now I have a happy Nybble! Untitled

That’s generous of you, but unnecessary. Thanks for helping me troubleshoot. If you can suggest a replacement, I’m happy to order it. I’ll let you know if it solves the problem!

Thank you so much Rongzhong – I know you're busy with Bittle! When I restart with the uploader attached only to my Mac, I don't see it in the Arduino ports list. If I unplug it and reconnect, it appears in ports, but I get the same error message when I try to upload, and it gets hot. Perhaps I fried the uploader? At one point I received a warning that the usb device was drawing too much power, so I've only connected with batteries attached and servos powered since then. Thanks for the advice.