Veteran's 3rd "THE ULTIMATE CUSTOM BUILD"

[erik_gee]

Hey one thing i realized is that on the ads1115 boards they have pull-up resistors on the sda and scl lines so if you power the module from 5v these lines will have the pi's pull-ups to 3v3 and also the modules to 5v. Not sure how this might affect things but might be a good idea to cut those traces on the module or desolder the resistors. What complicates this a bit more is that a logic high for the ads1115 is stated as .7*Vdd in the datasheet which would be 3.5v at Vdd=5v which is higher than the 3.3v logic on the pi. I have gotten away with it so far on my setup but it is out of spec so there's no guarantees.

Are you saying that powering the ads1115 at 5v vdd will cause the output voltage on the sda and scl to be above 3.3v and damage the pi ?

[erik_gee]

If that is the case, then I would recommend to those reading to creat a voltage divider with a 10k and 5k resistor pair. Use the 5v source and the output will be a rough 3.3v , falling within spec hopefully this can help someone out

[BadBert]

this build is awsome.
very clean!!!!

nice one!

[joeygbsn]

If that is the case, then I would recommend to those reading to creat a voltage divider with a 10k and 5k resistor pair. Use the 5v source and the output will be a rough 3.3v , falling within spec hopefully this can help someone out

I'm not sure if it will cause damage to the pi but you are only supposed to have one set of pull-ups on the i2c bus. Using a voltage divider doesn't really work for powering devices. When you use a voltage divider you assume the output is high impedance and won't draw any current. When you use the output to power a device you essentially have a lower impedance in parallel with the bottom 10k which changes the overall resistance and therefore changes the output voltage. Probably easier to just use the regulated 3v3 from the pi. If you use 3v3 as your Vdd you would then need a divider from the battery to the A0 input to keep the measured voltage below 3v3 as you can't measure higher than Vdd. I think just taking the pull-ups off and using 5v is easiest.

[VeteranGamer]

If that is the case, then I would recommend to those reading to creat a voltage divider with a 10k and 5k resistor pair. Use the 5v source and the output will be a rough 3.3v , falling within spec hopefully this can help someone out

I'm not sure if it will cause damage to the pi but you are only supposed to have one set of pull-ups on the i2c bus. Using a voltage divider doesn't really work for powering devices. When you use a voltage divider you assume the output is high impedance and won't draw any current. When you use the output to power a device you essentially have a lower impedance in parallel with the bottom 10k which changes the overall resistance and therefore changes the output voltage. Probably easier to just use the regulated 3v3 from the pi. If you use 3v3 as your Vdd you would then need a divider from the battery to the A0 input to keep the measured voltage below 3v3 as you can't measure higher than Vdd. I think just taking the pull-ups off and using 5v is easiest.

this is great info....

i think its best discussed in this post....

https://sudomod.com/forum/viewtopic.php?f=42&t=4585

and i'll update any finding here as well....

thanks

[erik_gee]

If that is the case, then I would recommend to those reading to creat a voltage divider with a 10k and 5k resistor pair. Use the 5v source and the output will be a rough 3.3v , falling within spec hopefully this can help someone out

I'm not sure if it will cause damage to the pi but you are only supposed to have one set of pull-ups on the i2c bus. Using a voltage divider doesn't really work for powering devices. When you use a voltage divider you assume the output is high impedance and won't draw any current. When you use the output to power a device you essentially have a lower impedance in parallel with the bottom 10k which changes the overall resistance and therefore changes the output voltage. Probably easier to just use the regulated 3v3 from the pi. If you use 3v3 as your Vdd you would then need a divider from the battery to the A0 input to keep the measured voltage below 3v3 as you can't measure higher than Vdd. I think just taking the pull-ups off and using 5v is easiest.

this is great info....

i think its best discussed in this post....

https://sudomod.com/forum/viewtopic.php?f=42&t=4585

and i'll update any finding here as well....

thanks

A lot of information there but doesn't seem to cover this topic unfortunately. But since the person on that thread got it working, perhaps the pull resistors aren't as big of a deal as we are making it?

[erik_gee]

If that is the case, then I would recommend to those reading to creat a voltage divider with a 10k and 5k resistor pair. Use the 5v source and the output will be a rough 3.3v , falling within spec hopefully this can help someone out

I'm not sure if it will cause damage to the pi but you are only supposed to have one set of pull-ups on the i2c bus. Using a voltage divider doesn't really work for powering devices. When you use a voltage divider you assume the output is high impedance and won't draw any current. When you use the output to power a device you essentially have a lower impedance in parallel with the bottom 10k which changes the overall resistance and therefore changes the output voltage. Probably easier to just use the regulated 3v3 from the pi. If you use 3v3 as your Vdd you would then need a divider from the battery to the A0 input to keep the measured voltage below 3v3 as you can't measure higher than Vdd. I think just taking the pull-ups off and using 5v is easiest.

Ah I see what you are saying now. My mistake.
I believe someone else on the thread veteran posted used an ADC module without touching the pull ups on sda and scl lines, and worked for him. He didn't state what vdd he was using, whether it was 3.3 or 5 though.

The pi's pins can't accept a voltage higher than 3.3 or they will fry, so I thought that's what you were getting at. But now that I think about it, since you said the voltage is at .7vdd, then maybe we can still use the 5v power source, and then use a diode to drop it .5v? Then you would have roughly 3.1v for the output, but since the Vdd is 4.5v, you'll still have the range for a0 input. Sorry my knowledge is lacking a bit in this area, hopefully I don't sound stupid haha

[erik_gee]

Woops I mean .7v. not .5 but still same concept. Should allow the range of the battery voltage for a0 without the need of a voltage divider and still provide enough power for the module

[joeygbsn]

Woops I mean .7v. not .5 but still same concept. Should allow the range of the battery voltage for a0 without the need of a voltage divider and still provide enough power for the module

Continuing this conversation on the other thread.

https://sudomod.com/forum/viewtopic.php?f=42&t=4585

[Dr0Heaven]

Hy what Typ of LEDs are you useing?
Do i Need to add something on the Skript ?
Best regards