Forums

i2c pull up resistor situation

Started by bitrex June 11, 2020
These little "Digistump" Velleman boards with an ATTiny85 on them are 
handy, but because they're intended to be programmed directly over USB
compromises have to be made:

<https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf>

The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying 
to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to 
work with the stock pull-ups that come on many "breakout boards" 
pre-built for i2c devices due to the inline resistor/diode combination 
on D-. Looking for advice on if that's possible and set of appropriate 
values to bodge in as I don't have the time to cut-n-try!

I'm trying to get 2 software/bit-bang i2c devices running off it and 
pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible 
options for the pairs with the ADC on PB3 spoken for, and the resistor 
and LED on PB1.

Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a 
fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's 
still configured as a reset pin, and have to use another programmer to 
set the fuses to enable it.
On 6/11/2020 1:08 PM, bitrex wrote:
> These little "Digistump" Velleman boards with an ATTiny85 on them are > handy, but because they're intended to be programmed directly over USB > compromises have to be made: > > <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> > > The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying > to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to > work with the stock pull-ups that come on many "breakout boards" > pre-built for i2c devices due to the inline resistor/diode combination > on D-. Looking for advice on if that's possible and set of appropriate > values to bodge in as I don't have the time to cut-n-try! > > I'm trying to get 2 software/bit-bang i2c devices running off it and > pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible > options for the pairs with the ADC on PB3 spoken for, and the resistor > and LED on PB1. > > Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a > fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's > still configured as a reset pin, and have to use another programmer to > set the fuses to enable it.
Correction, one of the devices is not strictly i2c, it's a dumb two-wire serial protocol for the "tm1637" display controller. If it were "real" i2c it would be easy as one would not respond to the other's address and could hang them on the same pins as two independent slaves and wouldn't interfere with each other.
On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote:
> These little "Digistump" Velleman boards with an ATTiny85 on them are > handy, but because they're intended to be programmed directly over USB > compromises have to be made: > > <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> > > The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying > to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to > work with the stock pull-ups that come on many "breakout boards" > pre-built for i2c devices due to the inline resistor/diode combination > on D-. Looking for advice on if that's possible and set of appropriate > values to bodge in as I don't have the time to cut-n-try! > > I'm trying to get 2 software/bit-bang i2c devices running off it and > pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible > options for the pairs with the ADC on PB3 spoken for, and the resistor > and LED on PB1. > > Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a > fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's > still configured as a reset pin, and have to use another programmer to > set the fuses to enable it.
Sorry, but I'm not following what the problem is. You say D+ and PB5 can't be used because of the 66 ohm resistor and the Zener diode on the D+ line. I assume the Zener part number is a typo and should be BZT52C3V6 for a 3.6 volt zener. Otherwise it is a 36 volt Zener and is completely out of the loop. Still, the 3.6 volt zener should not cause problems since it doesn't draw much current until the signal level is at least 2.5 volts or higher. If you are pairing this signal with PB5 that means you are using J1 and so the resistor is out of the loop. Maybe your problem is elsewhere? -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
On 6/11/2020 2:38 PM, Ricketty C wrote:
> On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote: >> These little "Digistump" Velleman boards with an ATTiny85 on them are >> handy, but because they're intended to be programmed directly over USB >> compromises have to be made: >> >> <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> >> >> The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying >> to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to >> work with the stock pull-ups that come on many "breakout boards" >> pre-built for i2c devices due to the inline resistor/diode combination >> on D-. Looking for advice on if that's possible and set of appropriate >> values to bodge in as I don't have the time to cut-n-try! >> >> I'm trying to get 2 software/bit-bang i2c devices running off it and >> pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible >> options for the pairs with the ADC on PB3 spoken for, and the resistor >> and LED on PB1. >> >> Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a >> fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's >> still configured as a reset pin, and have to use another programmer to >> set the fuses to enable it. > > Sorry, but I'm not following what the problem is. You say D+ and PB5 can't be used because of the 66 ohm resistor and the Zener diode on the D+ line. I assume the Zener part number is a typo and should be BZT52C3V6 for a 3.6 volt zener. Otherwise it is a 36 volt Zener and is completely out of the loop. Still, the 3.6 volt zener should not cause problems since it doesn't draw much current until the signal level is at least 2.5 volts or higher. If you are pairing this signal with PB5 that means you are using J1 and so the resistor is out of the loop. Maybe your problem is elsewhere? >
Ah crap, yeah those are Zeners. I'm used to seeing the other symbol I misinterpreted that at first glance as Schottkys, I should have checked the part number. Right, that may be the problem, the signal for a 5 volt bus is getting clamped.
On 6/11/2020 2:47 PM, bitrex wrote:
> On 6/11/2020 2:38 PM, Ricketty C wrote: >> On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote: >>> These little "Digistump" Velleman boards with an ATTiny85 on them are >>> handy, but because they're intended to be programmed directly over USB >>> compromises have to be made: >>> >>> <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> >>> >>> The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying >>> to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to >>> work with the stock pull-ups that come on many "breakout boards" >>> pre-built for i2c devices due to the inline resistor/diode combination >>> on D-. Looking for advice on if that's possible and set of appropriate >>> values to bodge in as I don't have the time to cut-n-try! >>> >>> I'm trying to get 2 software/bit-bang i2c devices running off it and >>> pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible >>> options for the pairs with the ADC on PB3 spoken for, and the resistor >>> and LED on PB1. >>> >>> Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a >>> fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's >>> still configured as a reset pin, and have to use another programmer to >>> set the fuses to enable it. >> >> Sorry, but I'm not following what the problem is.&nbsp; You say D+ and PB5 >> can't be used because of the 66 ohm resistor and the Zener diode on >> the D+ line.&nbsp; I assume the Zener part number is a typo and should be >> BZT52C3V6 for a 3.6 volt zener.&nbsp; Otherwise it is a 36 volt Zener and >> is completely out of the loop.&nbsp; Still, the 3.6 volt zener should not >> cause problems since it doesn't draw much current until the signal >> level is at least 2.5 volts or higher.&nbsp; If you are pairing this signal >> with PB5 that means you are using J1 and so the resistor is out of the >> loop.&nbsp; Maybe your problem is elsewhere? >> > > Ah crap, yeah those are Zeners. I'm used to seeing the other symbol I > misinterpreted that at first glance as Schottkys, I should have checked > the part number. > > Right, that may be the problem, the signal for a 5 volt bus is getting > clamped.
These two symbols for Zener and Schottky are too much alike I never use that one for Zener in my own work so my brain just filled the rest in I guess. there should be a law! <https://cdn.instructables.com/FFQ/YA9J/H5R9ECF5/FFQYA9JH5R9ECF5.LARGE.gif?auto=webp&frame=1&fit=bounds>
On Thursday, June 11, 2020 at 2:56:42 PM UTC-4, bitrex wrote:
> On 6/11/2020 2:47 PM, bitrex wrote: > > On 6/11/2020 2:38 PM, Ricketty C wrote: > >> On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote: > >>> These little "Digistump" Velleman boards with an ATTiny85 on them are > >>> handy, but because they're intended to be programmed directly over USB > >>> compromises have to be made: > >>> > >>> <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> > >>> > >>> The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying > >>> to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to > >>> work with the stock pull-ups that come on many "breakout boards" > >>> pre-built for i2c devices due to the inline resistor/diode combination > >>> on D-. Looking for advice on if that's possible and set of appropriate > >>> values to bodge in as I don't have the time to cut-n-try! > >>> > >>> I'm trying to get 2 software/bit-bang i2c devices running off it and > >>> pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible > >>> options for the pairs with the ADC on PB3 spoken for, and the resistor > >>> and LED on PB1. > >>> > >>> Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a > >>> fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's > >>> still configured as a reset pin, and have to use another programmer to > >>> set the fuses to enable it. > >> > >> Sorry, but I'm not following what the problem is.&nbsp; You say D+ and PB5 > >> can't be used because of the 66 ohm resistor and the Zener diode on > >> the D+ line.&nbsp; I assume the Zener part number is a typo and should be > >> BZT52C3V6 for a 3.6 volt zener.&nbsp; Otherwise it is a 36 volt Zener and > >> is completely out of the loop.&nbsp; Still, the 3.6 volt zener should not > >> cause problems since it doesn't draw much current until the signal > >> level is at least 2.5 volts or higher.&nbsp; If you are pairing this signal > >> with PB5 that means you are using J1 and so the resistor is out of the > >> loop.&nbsp; Maybe your problem is elsewhere? > >> > > > > Ah crap, yeah those are Zeners. I'm used to seeing the other symbol I > > misinterpreted that at first glance as Schottkys, I should have checked > > the part number. > > > > Right, that may be the problem, the signal for a 5 volt bus is getting > > clamped. > > These two symbols for Zener and Schottky are too much alike I never use > that one for Zener in my own work so my brain just filled the rest in I > guess. there should be a law! > > <https://cdn.instructables.com/FFQ/YA9J/H5R9ECF5/FFQYA9JH5R9ECF5.LARGE.gif?auto=webp&frame=1&fit=bounds>
Technically I don't think that is a valid symbol at all. The Zener symbol uses 45 degree angle tips and the Schottky has angular curls a bit like the letter S. So this symbol is for an inside out tunnel diode or bidirectional step recovery diode. I don't know that it is clamped. The part number is actually for a 36 volt part. It depends on which is wrong, the part number or the intention of using a 36 volt part. USB is a 5 volt signaled bus, right? Or are the signal levels only 3.3 volts? I can't think why they are using 3.6 volt Zeners. -- Rick C. + Get 1,000 miles of free Supercharging + Tesla referral code - https://ts.la/richard11209
torsdag den 11. juni 2020 kl. 21.38.37 UTC+2 skrev Ricketty C:
> On Thursday, June 11, 2020 at 2:56:42 PM UTC-4, bitrex wrote: > > On 6/11/2020 2:47 PM, bitrex wrote: > > > On 6/11/2020 2:38 PM, Ricketty C wrote: > > >> On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote: > > >>> These little "Digistump" Velleman boards with an ATTiny85 on them are > > >>> handy, but because they're intended to be programmed directly over USB > > >>> compromises have to be made: > > >>> > > >>> <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> > > >>> > > >>> The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying > > >>> to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to > > >>> work with the stock pull-ups that come on many "breakout boards" > > >>> pre-built for i2c devices due to the inline resistor/diode combination > > >>> on D-. Looking for advice on if that's possible and set of appropriate > > >>> values to bodge in as I don't have the time to cut-n-try! > > >>> > > >>> I'm trying to get 2 software/bit-bang i2c devices running off it and > > >>> pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible > > >>> options for the pairs with the ADC on PB3 spoken for, and the resistor > > >>> and LED on PB1. > > >>> > > >>> Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a > > >>> fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's > > >>> still configured as a reset pin, and have to use another programmer to > > >>> set the fuses to enable it. > > >> > > >> Sorry, but I'm not following what the problem is.&nbsp; You say D+ and PB5 > > >> can't be used because of the 66 ohm resistor and the Zener diode on > > >> the D+ line.&nbsp; I assume the Zener part number is a typo and should be > > >> BZT52C3V6 for a 3.6 volt zener.&nbsp; Otherwise it is a 36 volt Zener and > > >> is completely out of the loop.&nbsp; Still, the 3.6 volt zener should not > > >> cause problems since it doesn't draw much current until the signal > > >> level is at least 2.5 volts or higher.&nbsp; If you are pairing this signal > > >> with PB5 that means you are using J1 and so the resistor is out of the > > >> loop.&nbsp; Maybe your problem is elsewhere? > > >> > > > > > > Ah crap, yeah those are Zeners. I'm used to seeing the other symbol I > > > misinterpreted that at first glance as Schottkys, I should have checked > > > the part number. > > > > > > Right, that may be the problem, the signal for a 5 volt bus is getting > > > clamped. > > > > These two symbols for Zener and Schottky are too much alike I never use > > that one for Zener in my own work so my brain just filled the rest in I > > guess. there should be a law! > > > > <https://cdn.instructables.com/FFQ/YA9J/H5R9ECF5/FFQYA9JH5R9ECF5.LARGE.gif?auto=webp&frame=1&fit=bounds> > > Technically I don't think that is a valid symbol at all. The Zener symbol uses 45 degree angle tips and the Schottky has angular curls a bit like the letter S. So this symbol is for an inside out tunnel diode or bidirectional step recovery diode. > > I don't know that it is clamped. The part number is actually for a 36 volt part. It depends on which is wrong, the part number or the intention of using a 36 volt part. > > USB is a 5 volt signaled bus, right? Or are the signal levels only 3.3 volts? I can't think why they are using 3.6 volt Zeners. >
USB signalling is 3.3V, the zeners (some have used blue leds instead) is a hack to do bit banged low speed 1.5Mb/s USB with an MCU running on ~5V
On Thursday, June 11, 2020 at 9:42:17 PM UTC-4, bitrex wrote:
> On 6/11/2020 3:45 PM, Lasse Langwadt Christensen wrote: > > torsdag den 11. juni 2020 kl. 21.38.37 UTC+2 skrev Ricketty C: > >> On Thursday, June 11, 2020 at 2:56:42 PM UTC-4, bitrex wrote: > >>> On 6/11/2020 2:47 PM, bitrex wrote: > >>>> On 6/11/2020 2:38 PM, Ricketty C wrote: > >>>>> On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote: > >>>>>> These little "Digistump" Velleman boards with an ATTiny85 on them are > >>>>>> handy, but because they're intended to be programmed directly over USB > >>>>>> compromises have to be made: > >>>>>> > >>>>>> <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> > >>>>>> > >>>>>> The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying > >>>>>> to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to > >>>>>> work with the stock pull-ups that come on many "breakout boards" > >>>>>> pre-built for i2c devices due to the inline resistor/diode combination > >>>>>> on D-. Looking for advice on if that's possible and set of appropriate > >>>>>> values to bodge in as I don't have the time to cut-n-try! > >>>>>> > >>>>>> I'm trying to get 2 software/bit-bang i2c devices running off it and > >>>>>> pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible > >>>>>> options for the pairs with the ADC on PB3 spoken for, and the resistor > >>>>>> and LED on PB1. > >>>>>> > >>>>>> Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a > >>>>>> fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's > >>>>>> still configured as a reset pin, and have to use another programmer to > >>>>>> set the fuses to enable it. > >>>>> > >>>>> Sorry, but I'm not following what the problem is.&nbsp; You say D+ and PB5 > >>>>> can't be used because of the 66 ohm resistor and the Zener diode on > >>>>> the D+ line.&nbsp; I assume the Zener part number is a typo and should be > >>>>> BZT52C3V6 for a 3.6 volt zener.&nbsp; Otherwise it is a 36 volt Zener and > >>>>> is completely out of the loop.&nbsp; Still, the 3.6 volt zener should not > >>>>> cause problems since it doesn't draw much current until the signal > >>>>> level is at least 2.5 volts or higher.&nbsp; If you are pairing this signal > >>>>> with PB5 that means you are using J1 and so the resistor is out of the > >>>>> loop.&nbsp; Maybe your problem is elsewhere? > >>>>> > >>>> > >>>> Ah crap, yeah those are Zeners. I'm used to seeing the other symbol I > >>>> misinterpreted that at first glance as Schottkys, I should have checked > >>>> the part number. > >>>> > >>>> Right, that may be the problem, the signal for a 5 volt bus is getting > >>>> clamped. > >>> > >>> These two symbols for Zener and Schottky are too much alike I never use > >>> that one for Zener in my own work so my brain just filled the rest in I > >>> guess. there should be a law! > >>> > >>> <https://cdn.instructables.com/FFQ/YA9J/H5R9ECF5/FFQYA9JH5R9ECF5.LARGE.gif?auto=webp&frame=1&fit=bounds> > >> > >> Technically I don't think that is a valid symbol at all. The Zener symbol uses 45 degree angle tips and the Schottky has angular curls a bit like the letter S. So this symbol is for an inside out tunnel diode or bidirectional step recovery diode. > >> > >> I don't know that it is clamped. The part number is actually for a 36 volt part. It depends on which is wrong, the part number or the intention of using a 36 volt part. > >> > >> USB is a 5 volt signaled bus, right? Or are the signal levels only 3.3 volts? I can't think why they are using 3.6 volt Zeners. > >> > > > > USB signalling is 3.3V, the zeners (some have used blue leds instead) is a hack to do bit banged low speed 1.5Mb/s USB with an MCU running on ~5V > > > > Do you see any "hacks" I could use to get two two-wire bit-bangers > running on this thing with 0.7*5 volt Vcc high threshold without an > external shifter? I'm not seeing it, unfortunately :(
You are using J1 to connect your two-wire devices, no? Remove R4 and D+ is now free to rise. Or remove the Zener diodes. Is that not an option? You really have not explained very much about what is going on with your design. -- Rick C. -- Get 1,000 miles of free Supercharging -- Tesla referral code - https://ts.la/richard11209
On 6/11/2020 3:45 PM, Lasse Langwadt Christensen wrote:
> torsdag den 11. juni 2020 kl. 21.38.37 UTC+2 skrev Ricketty C: >> On Thursday, June 11, 2020 at 2:56:42 PM UTC-4, bitrex wrote: >>> On 6/11/2020 2:47 PM, bitrex wrote: >>>> On 6/11/2020 2:38 PM, Ricketty C wrote: >>>>> On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote: >>>>>> These little "Digistump" Velleman boards with an ATTiny85 on them are >>>>>> handy, but because they're intended to be programmed directly over USB >>>>>> compromises have to be made: >>>>>> >>>>>> <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> >>>>>> >>>>>> The 1.5k pullup on the ADC input pin "D-" can be worked around. Trying >>>>>> to run low-speed software i2c over pin "D+" and PB5/nRES doesn't seem to >>>>>> work with the stock pull-ups that come on many "breakout boards" >>>>>> pre-built for i2c devices due to the inline resistor/diode combination >>>>>> on D-. Looking for advice on if that's possible and set of appropriate >>>>>> values to bodge in as I don't have the time to cut-n-try! >>>>>> >>>>>> I'm trying to get 2 software/bit-bang i2c devices running off it and >>>>>> pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible >>>>>> options for the pairs with the ADC on PB3 spoken for, and the resistor >>>>>> and LED on PB1. >>>>>> >>>>>> Frustratingly the Chinese knock-offs of the Digistump (and Velleman is a >>>>>> fashion of that) don't come with PB5/nRES enabled as an IO, stock, it's >>>>>> still configured as a reset pin, and have to use another programmer to >>>>>> set the fuses to enable it. >>>>> >>>>> Sorry, but I'm not following what the problem is.&nbsp; You say D+ and PB5 >>>>> can't be used because of the 66 ohm resistor and the Zener diode on >>>>> the D+ line.&nbsp; I assume the Zener part number is a typo and should be >>>>> BZT52C3V6 for a 3.6 volt zener.&nbsp; Otherwise it is a 36 volt Zener and >>>>> is completely out of the loop.&nbsp; Still, the 3.6 volt zener should not >>>>> cause problems since it doesn't draw much current until the signal >>>>> level is at least 2.5 volts or higher.&nbsp; If you are pairing this signal >>>>> with PB5 that means you are using J1 and so the resistor is out of the >>>>> loop.&nbsp; Maybe your problem is elsewhere? >>>>> >>>> >>>> Ah crap, yeah those are Zeners. I'm used to seeing the other symbol I >>>> misinterpreted that at first glance as Schottkys, I should have checked >>>> the part number. >>>> >>>> Right, that may be the problem, the signal for a 5 volt bus is getting >>>> clamped. >>> >>> These two symbols for Zener and Schottky are too much alike I never use >>> that one for Zener in my own work so my brain just filled the rest in I >>> guess. there should be a law! >>> >>> <https://cdn.instructables.com/FFQ/YA9J/H5R9ECF5/FFQYA9JH5R9ECF5.LARGE.gif?auto=webp&frame=1&fit=bounds> >> >> Technically I don't think that is a valid symbol at all. The Zener symbol uses 45 degree angle tips and the Schottky has angular curls a bit like the letter S. So this symbol is for an inside out tunnel diode or bidirectional step recovery diode. >> >> I don't know that it is clamped. The part number is actually for a 36 volt part. It depends on which is wrong, the part number or the intention of using a 36 volt part. >> >> USB is a 5 volt signaled bus, right? Or are the signal levels only 3.3 volts? I can't think why they are using 3.6 volt Zeners. >> > > USB signalling is 3.3V, the zeners (some have used blue leds instead) is a hack to do bit banged low speed 1.5Mb/s USB with an MCU running on ~5V > > > > > >
Do you see any "hacks" I could use to get two two-wire bit-bangers running on this thing with 0.7*5 volt Vcc high threshold without an external shifter? I'm not seeing it, unfortunately :(
On 6/12/2020 1:42 AM, bitrex wrote:
> On 6/11/2020 3:45 PM, Lasse Langwadt Christensen wrote: >> torsdag den 11. juni 2020 kl. 21.38.37 UTC+2 skrev Ricketty C: >>> On Thursday, June 11, 2020 at 2:56:42 PM UTC-4, bitrex wrote: >>>> On 6/11/2020 2:47 PM, bitrex wrote: >>>>> On 6/11/2020 2:38 PM, Ricketty C wrote: >>>>>> On Thursday, June 11, 2020 at 1:08:12 PM UTC-4, bitrex wrote: >>>>>>> These little "Digistump" Velleman boards with an ATTiny85 on them >>>>>>> are >>>>>>> handy, but because they're intended to be programmed directly >>>>>>> over USB >>>>>>> compromises have to be made: >>>>>>> >>>>>>> <https://www.velleman.eu/downloads/29/infosheets/vma108_scheme.pdf> >>>>>>> >>>>>>> The 1.5k pullup on the ADC input pin "D-" can be worked around. >>>>>>> Trying >>>>>>> to run low-speed software i2c over pin "D+" and PB5/nRES doesn't >>>>>>> seem to >>>>>>> work with the stock pull-ups that come on many "breakout boards" >>>>>>> pre-built for i2c devices due to the inline resistor/diode >>>>>>> combination >>>>>>> on D-. Looking for advice on if that's possible and set of >>>>>>> appropriate >>>>>>> values to bodge in as I don't have the time to cut-n-try! >>>>>>> >>>>>>> I'm trying to get 2 software/bit-bang i2c devices running off it and >>>>>>> pins PB0 and PB2 and pins PB4 and PB5 look like my only plausible >>>>>>> options for the pairs with the ADC on PB3 spoken for, and the >>>>>>> resistor >>>>>>> and LED on PB1. >>>>>>> >>>>>>> Frustratingly the Chinese knock-offs of the Digistump (and >>>>>>> Velleman is a >>>>>>> fashion of that) don't come with PB5/nRES enabled as an IO, >>>>>>> stock, it's >>>>>>> still configured as a reset pin, and have to use another >>>>>>> programmer to >>>>>>> set the fuses to enable it. >>>>>> >>>>>> Sorry, but I'm not following what the problem is.&nbsp; You say D+ and PB5 >>>>>> can't be used because of the 66 ohm resistor and the Zener diode on >>>>>> the D+ line.&nbsp; I assume the Zener part number is a typo and should be >>>>>> BZT52C3V6 for a 3.6 volt zener.&nbsp; Otherwise it is a 36 volt Zener and >>>>>> is completely out of the loop.&nbsp; Still, the 3.6 volt zener should not >>>>>> cause problems since it doesn't draw much current until the signal >>>>>> level is at least 2.5 volts or higher.&nbsp; If you are pairing this >>>>>> signal >>>>>> with PB5 that means you are using J1 and so the resistor is out of >>>>>> the >>>>>> loop.&nbsp; Maybe your problem is elsewhere? >>>>>> >>>>> >>>>> Ah crap, yeah those are Zeners. I'm used to seeing the other symbol I >>>>> misinterpreted that at first glance as Schottkys, I should have >>>>> checked >>>>> the part number. >>>>> >>>>> Right, that may be the problem, the signal for a 5 volt bus is getting >>>>> clamped. >>>> >>>> These two symbols for Zener and Schottky are too much alike I never use >>>> that one for Zener in my own work so my brain just filled the rest in I >>>> guess. there should be a law! >>>> >>>> <https://cdn.instructables.com/FFQ/YA9J/H5R9ECF5/FFQYA9JH5R9ECF5.LARGE.gif?auto=webp&frame=1&fit=bounds> >>>> >>> >>> Technically I don't think that is a valid symbol at all.&nbsp; The Zener >>> symbol uses 45 degree angle tips and the Schottky has angular curls a >>> bit like the letter S.&nbsp; So this symbol is for an inside out tunnel >>> diode or bidirectional step recovery diode. >>> >>> I don't know that it is clamped.&nbsp; The part number is actually for a >>> 36 volt part.&nbsp; It depends on which is wrong, the part number or the >>> intention of using a 36 volt part. >>> >>> USB is a 5 volt signaled bus, right?&nbsp; Or are the signal levels only >>> 3.3 volts?&nbsp; I can't think why they are using 3.6 volt Zeners. >>> >> >> USB signalling is 3.3V, the zeners (some have used blue leds instead) >> is a hack to do bit banged low speed 1.5Mb/s USB with an MCU running >> on ~5V >> >> >> >> >> >> > > Do you see any "hacks" I could use to get two two-wire bit-bangers > running on this thing with 0.7*5 volt Vcc high threshold without an > external shifter? I'm not seeing it, unfortunately :(
Series diode would probably work to bring it up above the threshold if I keep it slow, I guess.