USB µISP

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I'd like to just make a quick mention of my humble little AVR programmer that I sell on Tindie. I call it the USB µISP. It's a USBTiny clone, and its design came largely out of the AdaFruit USBTiny and the SparkFun Pocket AVR programmer. Like the SparkFun version, it's SMD, so it's small, and it has a PolyFuse on the USB power input. Like both programmers, it has a 74HC125 bus buffer chip. But when SparkFun added a pull-up resistor to the BUFFEN line, they created a target power "leak" path, which makes theirs unsafe for 3.3 volt targets (that could be damaged by 5 volt power). My design has blocking diodes to prevent this. I also added a 3.3 volt LDO, and a target power jumper block so that the target can either be supplied with 3.3 volt power, 5 volt power, or no power (meaning the target it self-powered during programming). The USB connector is the more commonplace micro-USB one instead of the mini-USB used by SparkFun. I also use the most recent v1.7 firmware from the original designer.

 

The next version - available next week - will add a current-limiting switch to the target power supply line, making it safe to "hot plug" targets (this is particularly helpful when using pogo pin programming jigs). I've still got a few boards left in inventory that don't have this feature (they work well, but sometimes the USB cable must be un- and re-plugged if hot-plugging the target), and am selling them at a 15% discount off the normal $16 price.

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To clear out the inventory of the old version, for this weekend, they're 25% off and with free domestic (US) shipping - a 3.3 volt or 5 volt agile USB connected AVR programmer for only $12. Come and get 'em!

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Looks like a nice little programmer, but for $12 I could buy 5 USBasps off aliexpress with free shipping.  I've used them not just for programmers, but also for usb-connected projects.

 

I have no special talents.  I am only passionately curious. - Albert Einstein

 

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Seriously? You can get them for $2.50ish with free shipping? I can't conceive of how they can economically offer that. Here, they're €9,90. Mine isn't that cheap normally, but I'd like to believe that the bulletproof design and multiple target power options and such offer added value.

 

Last Edited: Sat. Nov 22, 2014 - 06:16 PM
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Here's one example:

http://www.aliexpress.com/item/U...

That's with an on-board AMS1117 3.3V, with the jumper selecting between 5V and 3.3V for the target voltage.  This version lacks a cap on the output side of the 3.3V regulator, so I just soldered an 0805 .1uF cap between the 3.3V and ground leads on the regulator.

 

The 5V versions (no 3.3V regulator) are as cheap as $2.20:

http://www.aliexpress.com/item/F...

 

I have no special talents.  I am only passionately curious. - Albert Einstein

 

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Well, I personally don't see how they can sell them at that price unless they fell off the back of a truck. 

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nsayer wrote:
The next version ...
Thought about adding PDI?

The tiny313 has a USART.

PDI data is bi-directional so PDI on a separate connector (though there are other ways).

IIRC Dean's LUFA contains an example as a schematic for the AVRISP mkII clone.

TIA

"Dare to be naïve." - Buckminster Fuller

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gchapman wrote:

Thought about adding PDI?

 

The tiny313 has a USART.

PDI data is bi-directional so PDI on a separate connector (though there are other ways).

IIRC Dean's LUFA contains an example as a schematic for the AVRISP mkII clone.

TIA

 

I certainly don't mind. Those two pins are NC at the moment. I think the problem will likely be that there's very little room in flash for more stuff. The USBTinyISP program pretty much fills it up. You can check it out at Dick's site.

 

I've been tempted to switch from the ATTiny2313 to the ATTiny84 and use V-USB. That would certainly give more flash space, but alas, it would also make use of all of the tiny84's pins. You could, however, use soft serial (or equiv) and the MISO/MOSI pair for serial I/O in some sort of alternate mode (or with alternate firmware). No telling whether that would work in concert with V-USB, though.

 

 

 

 

 

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nsayer wrote:

Well, I personally don't see how they can sell them at that price unless they fell off the back of a truck. 

 

In 1K volumes it's easy:

PCB: 10c

USB connector: 5c

12Mhz xtal: 5c

passives & LEDs: 10c

AtMega8a: 50c

10-pin connector & ribbon cable: 10c

assemble & test: 15c

packaging: 5c

total: 110c

 

The manufacturer can sell it to the reseller for 138c, making a 25% margin.  The seller gets $1.80 ea (30% margin) assuming $2 for shipping - Chinese logistics companies like espeedpost charge around $18/kg for China/HK post mail.

 

I suspect the Mega8A may be even cheaper than 50c ea; a visit to the SEG Electronics Market would give you a good idea of Shenzhen pricing.

 

I have no special talents.  I am only passionately curious. - Albert Einstein

 

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For what it's worth, I'm spinning up a new revision to this that adds a recovery clock pin and swaps out the header/jumper voltage selection for a SP3T switch.

 

The recovery clock pin simply outputs a 500 kHz square wave (on the target Vcc) during programming. If you've incorrectly fused your AVR for an external crystal that isn't there, you can apply the recovery clock to one or other of the XTAL pins and set the fuses back to normal. Of course, if you disable RESET, then HVP is your only option. I haven't tried this with every possible fusing option, but in a quick test with an ATTiny85, it worked so long as you slowed down the SPI clock (probably just so it had time to come up once the clock was supplied) with -B 250.

 

The TXD and RXD pins are still NC, but again, there's no room left in the flash to use them for anything.

Last Edited: Wed. Feb 25, 2015 - 11:44 PM