Unable to use 3V circuit with USBtinyISP, its providing 4V o

USB AVR Programmer and SPI interface. Adafruit's USBtinyISP.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
dparson
 
Posts: 7
Joined: Sat Jan 18, 2014 4:55 am

Unable to use 3V circuit with USBtinyISP, its providing 4V o

Post by dparson »

Hi I'm trying to use the USBtinyISP with a breadboard circuit powered with a 3V battery pack but when plugging in the ISP with the JP3 power jumper removed, the circuit is receiving 4V from the ISP. Besides this one issue the ISP is working fine, it programs an ATtiny85 and can change fuse bits successfully. It also provides 5V to the breadboard when the JP3 power jumper is attached, so that is also working as expected. The only problem is with the JP3 power jumper removed and when I power the circuit with a 3V battery, the circuit instead receives 4V and if I probe the power and GND pins on the programming cable, confirmed it's the ISP providing this voltage. I can actually switch off the battery pack and the ISP continues to power the circuit.

I probed my soldering job and can't figure out what I messed up so hope a second pair of eyes can help or if the ISP is working as designed and I'm just using it in the wrong way. I have a nRF24L01+ wireless transceiver that I want to learn how to use and it supports no more than 3.6V on its VCC pin, so that's why I'm trying to setup a 3V circuit on the breadboard with an ATtiny85 as the microcontroller and USBtinyISP as the in-circuit programmer. But since the ISP is outputting 4V I'm stuck.

Below are answers to all the questions with pictures and a video showing the breadboard setup and the issue. If you have any ideas or suggestions that would be great, thanks!

FIRST: Are you using a USBtiny from a kit or from DIY? Make sure you mention that in your post
Kit purchased from adafruit.

SECOND: What OS and computer are you using?
Windows 7 on a Lenovo x130e netbook.

THIRD: Which programming software are you using, and what chip?
Arduino IDE with an ATtiny85.

FOURTH: Did the USBtinyISP ever work (even once) or is it your first time trying to talk to a chip?
Programming works with the JP3 jumper installed. Programming also works when powering the circuit with a 3V battery pack and with the JP3 jumper removed, but in this configuration the circuit voltage is at 4V rather than the 3V that the battery pack provides. When the JP3 jumper is removed and the battery pack is switched off, the microcontroller still runs an LED blink program, but in this configuration programming does not work.

FIFTH: Post screenshots (NOT copy&paste) of what is happening.
Video showing the issue: http://youtu.be/YzcgP8YvLBY

SIXTH: Post clear, in-focus, not-blurry, easy to see photos of the top and bottom of the kit. If the photos are blurry, unfocused, and difficult to see they will only make it harder to debug what is going on.
UsbTinyISP 1.jpg
UsbTinyISP 1.jpg (382.12 KiB) Viewed 688 times
UsbTinyISP 2.JPG
UsbTinyISP 2.JPG (262.99 KiB) Viewed 688 times

User avatar
adafruit_support_rick
 
Posts: 35092
Joined: Tue Mar 15, 2011 11:42 am

Re: Unable to use 3V circuit with USBtinyISP, its providing

Post by adafruit_support_rick »

The power jumper only disconnects the POWER pin on the ICPS header. There will still be 5V signals on the other pins. Are you saying that you are seeing 4V on the ICPS power pin, or just on some other pins?

Your build looks OK

User avatar
dparson
 
Posts: 7
Joined: Sat Jan 18, 2014 4:55 am

Re: Unable to use 3V circuit with USBtinyISP, its providing

Post by dparson »

It's interesting that the USBtinyISP would still use 5V for the other pins but diving deeper into the 74HC125 datasheet and reading this long explanation https://www.adafruit.com/forums/viewtop ... 443#p54659 I'm beginning to understand why, so thanks for that note.

I'm actually seeing 4.5V on pin2 of JP1, the ICSP power pin, when I have the JP3 power jumper removed.
UsbTinyISP 4.JPG
UsbTinyISP 4.JPG (73.8 KiB) Viewed 673 times
And the normal 5V when the jumper is installed.
UsbTinyISP 3.JPG
UsbTinyISP 3.JPG (71.82 KiB) Viewed 673 times

User avatar
adafruit_support_rick
 
Posts: 35092
Joined: Tue Mar 15, 2011 11:42 am

Re: Unable to use 3V circuit with USBtinyISP, its providing

Post by adafruit_support_rick »

There just isn't anyplace for that to come from, unless the 74HC125 is shorted out somehow. It's the only active component attached to that pin.

If you email [email protected] with a link to this thread, they may be able to get you a new one.

User avatar
dparson
 
Posts: 7
Joined: Sat Jan 18, 2014 4:55 am

Re: Unable to use 3V circuit with USBtinyISP, its providing

Post by dparson »

Thank you, I sent the email so we'll see what they say.

Locked
Please be positive and constructive with your questions and comments.

Return to “USBtinyISP”