digispark ATTiny85 not running on independent power

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I acquired some attiny dev boards based on the digispark design from ebay.
Im having this issue where the program runs on the ISP programmer connected to my PC usb port but when powering it with a 9v power supply, does not run.

I have just started with the blink program. starts immediately when plugged into the 5v supply from the usb.

If i disconnect it and attempt to run it using 9v supply to the vin connector it does nothing on powering up.
It is noteworthy that there is a linear regulator as seen in the attached diagram but would only give 3.5 volts to the vcc on the t85 because of the 1.5v voltage drop as the specs require that the input be at least 2v above the target output.

But this is not the issue, 

When using a higher external supply on the vin, 4.9 volts is supplied to the vcc on the chip but it does nothing except show the power led.
Plug it back into the usb and it runs fine again.
Image result for digispark schematic

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Last Edited: Mon. Jun 18, 2018 - 10:15 AM
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Your /res pin is floating when you unplug your programming tool. Tie it to +Vcc via a 10K resistor.

 

extra. Is D3 really connected as per the schematic? I think it should have the anode connected to the USB connector.

 

 

 

 

Ross McKenzie, Melbourne Australia

Last Edited: Mon. Jun 18, 2018 - 06:06 AM
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ooow! now that sounds like a rookie mistake. i will give it a go when i get onto it next. Thanks.

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also see my extra comment in post #2

 

Ross McKenzie, Melbourne Australia

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you know i saw that too. It looks backwards right? this schematic is from digistump but maybe its a otherwise it would not get power from the usb but it does work.

From someone else playing around with usb and attiny. Look at D3
Image result for digispark schematic

 

Last Edited: Mon. Jun 18, 2018 - 06:16 AM
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so with the reset pin tied to vcc. Would that stop the programmer?

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D3 in post # 5 is correct. D3 in post # 1 is wrong.

 

If the reset pin is connected to Vcc via a 10K resistor, the programmer will operate perfectly well. The 10K resistor is mandatory.

 

 

 

 

Ross McKenzie, Melbourne Australia

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Thanks, seems odd there is not one there in the schematic. Will mark as a solution when i test it out a bit later on.

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funnily enough had the same issue with this STM8 dollar board until i fried it. Looks like same issue. no resistor on reset.

do the larger arduinos have this feature built in because I did not have this issue with my uno.

 

Last Edited: Mon. Jun 18, 2018 - 06:36 AM
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but maybe the STM8 just doesn't need it?

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awneil wrote:

but maybe the STM8 just doesn't need it?

But I was having the same issue before i fried it

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R1 in your schematic of post # 9 ties the reset line up to the Vcc.

 

Ross McKenzie, Melbourne Australia

This reply has been marked as the solution. 
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All (most?) AVR's have an internal weak pullup for the reset pin, and most people believe the extra pullup is only really needed in noisy environments and / or with long wires connected to the reset pin.

 

A lot of 8705 variants need a decoupling / buffer capacitor on the input for stability. Note that the schematics from posts #5 and #9 have an input capacitor for the voltage regulator, but post #1 does not.

Examples in the datasheet seem to recommend 330nF on the input for this particular regulator.

http://www.st.com/content/ccc/resource/technical/document/datasheet/41/4f/b3/b0/12/d4/47/88/CD00000444.pdf/files/CD00000444.pdf/jcr:content/translations/en.CD00000444.pdf

 

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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OK so the plot thickens and i am even more confused.

 

I tried pulling up the RESET to VCC to no effect.

 

I tested the board with a 9v cell on VIN and it works like a charm:

VIN = 8.7v - .17A

RESET = 3.1v

VCC = 4.9v

 

But the power supply that does not work:

 

VIN = 10.2v - 1.2A

RESET = 3.5v

VCC = 4.0v

 

Notice that with the 7805 makes only 4v from the 10v2/12A  but 5v from the 9v battery.

Now im thinking the chip is not getting enough power at 4v

 

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Paulvdh wrote:

All (most?) AVR's have an internal weak pullup for the reset pin, and most people believe the extra pullup is only really needed in noisy environments and / or with long wires connected to the reset pin.

 

A lot of 8705 variants need a decoupling / buffer capacitor on the input for stability. Note that the schematics from posts #5 and #9 have an input capacitor for the voltage regulator, but post #1 does not.

Examples in the datasheet seem to recommend 330nF on the input for this particular regulator.

http://www.st.com/content/ccc/resource/technical/document/datasheet/41/4f/b3/b0/12/d4/47/88/CD00000444.pdf/files/CD00000444.pdf/jcr:content/translations/en.CD00000444.pdf

 

Thanks,
That may explain those weird results im getting. 9v Battery seem to supply more power to the VCC even though its lower than my 10.2v power supply. See post #14

also yes. i thought i had stumbled across this before.

This from the ATTiny datasheet.

Last Edited: Mon. Jun 18, 2018 - 09:53 AM
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Paulvdh wrote:

All (most?) AVR's have an internal weak pullup for the reset pin, and most people believe the extra pullup is only really needed in noisy environments and / or with long wires connected to the reset pin.

 

A lot of 8705 variants need a decoupling / buffer capacitor on the input for stability. Note that the schematics from posts #5 and #9 have an input capacitor for the voltage regulator, but post #1 does not.

Examples in the datasheet seem to recommend 330nF on the input for this particular regulator.

http://www.st.com/content/ccc/resource/technical/document/datasheet/41/4f/b3/b0/12/d4/47/88/CD00000444.pdf/files/CD00000444.pdf/jcr:content/translations/en.CD00000444.pdf

 

SOLVED.

Although im not complete certain was has gone on here but it turns out i needed a huge 47MF cap across the the power supply input. so im putting this down to a very wobbly power circuit from this old uniden wall supply.

Thanks to everone that lent their advice, i have learned a whole lot more about this stuff now.

Cheers

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47MF (mega farad) really would be huuuuuuuuuuuuuuge!!

 

surprise

 

Presumably, you mean mF (milli farad) or µF (micro farad) ?

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awneil wrote:

47MF (mega farad) really would be huuuuuuuuuuuuuuge!!

 

surprise

 

Presumably, you mean mF (milli farad) or µF (micro farad) ?


Yeah as big as a house right. Sorry yes the µF one

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so im putting this down to a very wobbly power circuit from this old uniden wall supply.

If it's a conventional step-down transformer power supply ('wall-wart' or similar), and is very old, then the filter capacitors may be well past their 'best before' date, and could be providing very little filtering.  Or, there may be no filter capacitors at all.

 

Put a scope on the output of that power supply, both with and without a load.  I expect you'll see deep rippling.

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joeymorin wrote:

so im putting this down to a very wobbly power circuit from this old uniden wall supply.

If it's a conventional step-down transformer power supply ('wall-wart' or similar), and is very old, then the filter capacitors may be well past their 'best before' date, and could be providing very little filtering.  Or, there may be no filter capacitors at all.

 

Put a scope on the output of that power supply, both with and without a load.  I expect you'll see deep rippling.


I did not get around to putting it on a scope but you are probably right. Quite specific supply could even be the filter was on the device side