Raspberry Pi 4 Won't Boot While PH4502c Is Connected To ADS1115

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Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

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12 posts • Page 1 of 1 QuarkSolution Posts: 7 Joined: Thu Oct 29, 2020 1:03 pm

Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 12:52 am

I have the analog pH sensor connected to my ADS1115. As long as it is connected, my RPi won't boot. As soon as I unplug the data pin of the sensor, RPi boots up. Once it's all booted up, I can connect it again, and my script can read the sensor voltage output and everything. I have made a voltage divider so that the sensor voltage don't go above 3V, I tried various combinations of resistors for that, none could make the RPi boot. What's more interesting is, once the sensor is connected after booting my RPi, the RPi survives a normal reboot; it will boot up as long as the sensor was connected after an initial cold boot. But if I unplug the power brick of my RPi, the same problem crops up again, and I have to disconnect the sensor to make my RPi boot. Image pcmanbob Posts: 13765 Joined: Fri May 31, 2013 9:28 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 9:32 am

Hi. So my first thought would be power supply. When you pi will not boot with the sensor connected what is the red LED on the pi doing ? When you reconnect your sensor after booting do you get a low voltage warning ( yellow lightening flash on desktop ) ? We want information… information… information........................no information no help The use of crystal balls & mind reading are not supported QuarkSolution Posts: 7 Joined: Thu Oct 29, 2020 1:03 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 12:46 pm

When the RPi won't boot, the LED glows solid red. When I reconnect the sensor after boot, I don't get low voltage warning, no flashing yellow lightning shows up. pcmanbob Posts: 13765 Joined: Fri May 31, 2013 9:28 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 12:51 pm

Ok so were are you unplugging the data pin of the sensor from the sensor its self or just from the ADC, in other words is the sensor output still connected to the 2 resistors and the pi ground, when the pi wont boot. We want information… information… information........................no information no help The use of crystal balls & mind reading are not supported QuarkSolution Posts: 7 Joined: Thu Oct 29, 2020 1:03 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 1:20 pm

I am just unplugging the brown wire in the picture. So, only the connection from the voltage divider to the ADC is what I am unplugging, everything else, including the sensor output to the two resistors and the pi ground is still connected. And as soon as I unplug the connection from the two resistors to the ADC, the RPi boots up. pcmanbob Posts: 13765 Joined: Fri May 31, 2013 9:28 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 1:41 pm

What happens if you connect the ADC terminal A3 in your diagram to 3.3V , will the pi boot then ? We want information… information… information........................no information no help The use of crystal balls & mind reading are not supported QuarkSolution Posts: 7 Joined: Thu Oct 29, 2020 1:03 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 1:59 pm

Yes, it does boot up when I connect A3 to the 3.3V rail. pcmanbob Posts: 13765 Joined: Fri May 31, 2013 9:28 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 2:08 pm

So the ADC part of the circuit is correct, what measured voltage do you have at the point between the 2 resistors between the probe Po and ground ? It might be time for you to post some actual pictures of your layout so we can see if you have got a wiring error. I suggest you upload them to imgur.com and just post links , will prevent problems with image sizing. We want information… information… information........................no information no help The use of crystal balls & mind reading are not supported trejan Posts: 7827 Joined: Tue Jul 02, 2019 2:28 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 2:59 pm

You can't wire the sensor like that. It has a permanent 5V connection which means the output always has a voltage but the ADC is only powered when the Pi is powered. The ADC datasheet says the analog inputs have a maximum of VDD + 0.3V but if VDD is 0V then anything above 0.3V is exceeding the limits and the ESD protection diodes on the inputs will start conduct. This causes a small voltage to appear on the 3.3V line which then causes the PMIC to refuse to start because it will check that all outputs are 0V before starting. The guides online for that sensor were written for older Pi models which didn't have the PMIC. They're still exceeding the limits of the ADC though. You need to only power the sensor when the Pi is on so use a transistor. QuarkSolution Posts: 7 Joined: Thu Oct 29, 2020 1:03 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Fri Oct 30, 2020 5:10 pm

It has a permanent 5V connection which means the output always has a voltage but the ADC is only powered when the Pi is powered.
- Both the sensor and the ADC are powered by the Pi, I am using the 5V output from the Pi to power the sensor. I cannot imagine why the sensor would always have a 5V power before the Pi itself is powered. Is it a microsecond difference where the Pi turns on the sensor BEFORE it turns on the ADC that's causing the problem?
what measured voltage do you have at the point between the 2 resistors between the probe Po and ground ?
- The voltage between the two ends of the brown wire in the diagram is 1,98V. I am using two 220 Ohm resistors, so the raw output of the sensor voltage would be 2X 1,98V (from Po to GND).
It might be time for you to post some actual pictures of your layout so we can see if you have got a wiring error.
- I would, but the breadboard is a rat's nest. I will also include a video so that it might be easier to understand. Video: https://imgur.com/Xuzrv96 Images: https://imgur.com/a/7v1ZnSP I made a mistake before shooting the video and taking the photos because I disconnected a bunch of wires to make it less of a rat's nest, the GND connection for the sensor was correctly connected before, I noticed I made that mistake after the videos were already uploaded. CORRECT VIDEO (tested it, still same problem): https://imgur.com/a/xs29juc Last edited by QuarkSolution on Fri Oct 30, 2020 5:20 pm, edited 1 time in total. pcmanbob Posts: 13765 Joined: Fri May 31, 2013 9:28 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Sat Oct 31, 2020 9:33 am

QuarkSolution wrote: ↑Fri Oct 30, 2020 5:10 pm - Both the sensor and the ADC are powered by the Pi, I am using the 5V output from the Pi to power the sensor. I cannot imagine why the sensor would always have a 5V power before the Pi itself is powered.
Because the 5v gpio header pin is connected directly to the usb power port so it will get power before the pi has had a change to start booting. you can prove this . remove the wire from the probe output that goes to the resistors ( at the probe end ) and connect this to the 5V rail on your bread board then try booting your pi. I think as trejan suggests you will find it prevents your pi from booting. We want information… information… information........................no information no help The use of crystal balls & mind reading are not supported QuarkSolution Posts: 7 Joined: Thu Oct 29, 2020 1:03 pm

Re: Raspberry Pi 4 won't boot while pH4502c is connected to ADS1115

Thu Nov 05, 2020 3:52 pm

Apologies for the late reply, but thank you pcmanbob! All I needed to know was this:
Because the 5v gpio header pin is connected directly to the usb power port so it will get power before the pi has had a change to start booting.
The ADC is rated for up to 5.5V power, and the simple fix to my problem was just connecting the ADS1115 VDD pin to the 5V rail, instead of 3.3V rail. I had forgotten to post the fix before, but now anyone else with this problem can find the solution online (surprisingly, there wasn't one before this one). Display posts from previous:All posts1 day7 days2 weeks1 month3 months6 months1 yearSort byAuthorPost timeSubjectAscendingDescending Locked
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