I built my USBtinyISP without any trouble and it seems to work most of the time, except for an occasional 'broken pipe' error when I use it with Arduino IDE. But mostly it works great.
The problem I'm having is there seems to be a voltage at the output whether the jumper is connected or not. I had it connected to an unpowered Arduino UNO, and if the jumper is connected, there's 5vdc at the VCC pinout. But if I remove the jumper, there's about 3.6vdc at the VCC pinout on the unpowered Arduino. Is this normal? Will I run into trouble if I use external power on my target? Thanks in advance for your help!
Voltage out with or without jumper
Moderators: adafruit_support_bill, adafruit
Please be positive and constructive with your questions and comments.
- phild13
- Posts: 247
- Joined: Mon Sep 10, 2012 1:05 pm
Re: Voltage out with or without jumper
Yes that is normal.
From the FAQ:
From the FAQ:
So it supplies 5v if the jumper is in place and 3.3v if the jumper is not in place.Version 2.0 which is almost certainly what you've got, uses a level shifter so that if the jumper is not in place, it will use whatever the target voltage is, a lot better for your low-voltage devices!
So, if you have a device that needs to run at 3.3V, don't have the jumper in place!
- peterinaz
- Posts: 13
- Joined: Wed Jun 05, 2013 12:18 am
Re: Voltage out with or without jumper
Thanks! I did read that part in the F.A.Q., but misunderstood. I thought it meant that low-voltage targets had to be self powered! Now all is right with the world again!
-
- Posts: 11
- Joined: Tue Sep 03, 2013 2:04 pm
Re: Voltage out with or without jumper
I do not think it supplies 3.3V, the programmer only accepts it and can work with it... Correct me if I'm wrong though!PhilD13 wrote:Yes that is normal.
From the FAQ:So it supplies 5v if the jumper is in place and 3.3v if the jumper is not in place.Version 2.0 which is almost certainly what you've got, uses a level shifter so that if the jumper is not in place, it will use whatever the target voltage is, a lot better for your low-voltage devices!
So, if you have a device that needs to run at 3.3V, don't have the jumper in place!
But that's my understanding of that explanation, meaning that the voltage that you have should not be there. Can't try it out right now. I'm pretty sure it shouldn't be supplied by the programmer, but by an external source.
- phild13
- Posts: 247
- Joined: Mon Sep 10, 2012 1:05 pm
Re: Voltage out with or without jumper
@sb555
You are correct. I did not take the time to look first before answering.
See:
http://www.ladyada.net/images/usbtinyis ... sp2sch.png
Edit:
Pin 2 on both ISP connectors feed VCC (pin 14) to the 74AHC125N. When the jumper is not installed the 74AHC125N will be powered
by the target. So to use with a 3.3 volt target the target has to be powered
You are correct. I did not take the time to look first before answering.
See:
http://www.ladyada.net/images/usbtinyis ... sp2sch.png
Edit:
Pin 2 on both ISP connectors feed VCC (pin 14) to the 74AHC125N. When the jumper is not installed the 74AHC125N will be powered
by the target. So to use with a 3.3 volt target the target has to be powered
-
- Posts: 11
- Joined: Tue Sep 03, 2013 2:04 pm
Re: Voltage out with or without jumper
Alright thenPhilD13 wrote:@sb555
You are correct. I did not take the time to look first before answering.
See:
http://www.ladyada.net/images/usbtinyis ... sp2sch.png
Edit:
Pin 2 on both ISP connectors feed VCC (pin 14) to the 74AHC125N. When the jumper is not installed the 74AHC125N will be powered
by the target. So to use with a 3.3 volt target the target has to be powered
Please be positive and constructive with your questions and comments.