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Ultimate GPS HAT
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Ultimate GPS HAT

by bri123 on Tue Apr 10, 2018 12:40 pm

I'm using an Adafruit Ultimate GPS Hat and a Olmatic S.USV Advanced Raspberry Pi UPS. The GPS Hat works fine on its own, as does the UPS. If I power on the Pi with the UPS attached and then plug the GPS hat into the UPS stack everything works fine. When I stack the GPS Hat on the UPS and then power on it freezes at the "rainbow screen". I'm assuming there is a current draw issue with both hats plugged in at power up.

Is there any solution to this problem besides removing the GPS hat before powering on?

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Re: Ultimate GPS HAT

by adafruit_support_mike on Thu Apr 12, 2018 1:53 am

I'm afraid we don't know anything about that UPS, and I can't think of anything in the GPS Hat that would be likely to cause problems.

The GPS Hat's only pin connections are power and the GPIO Serial pins. Check the UPS documentation to see if it says anything about talking to the RasPi's Serial port at startup.

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Re: Ultimate GPS HAT

by bri123 on Mon Apr 16, 2018 11:37 am

These are the pins used by the UPS:
- Pin #02: DC Power +5V – Power supply
- Pin #03: GPIO 02 (SDA1, I2C) – I2C data line
- Pin #05: GPIO 03 (SCL1, I2C) – I2C clock line
- Pin #13: GPIO 27 (GPIO_GEN2) – Monitoring S.USV
- Pin #27: ID_SD (I2C ID EEPROM) – ID data line
- Pin #28: ID_SC (I2C ID EEPROM) – ID clock line

The GPS Hat states in the data sheet that it has an EEPROM connection but is not used. Could this be causing the Pi to hang at boot?

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Re: Ultimate GPS HAT

by adafruit_support_mike on Tue Apr 17, 2018 2:51 am

The EEPROM is required by the Hat standard, and won't keep the RasPi from booting.

Post a photo showing your RasPi with the UPS Hat connected please. The GPS Hat has lots of conductive pads on its underside, and those could be making contact with some part of the UPS. 800x600 images usually work best.

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Re: Ultimate GPS HAT

by bri123 on Tue Apr 17, 2018 1:41 pm

Here are a few pictures of the GPS and UPS hats stacked on the Pi. There does not appear to be any contact between the boards other than at the headers. When power is applied the power LED lights up solid and the data LED blinks twice and goes blank. The monitor, connected through HDMI, shows only the "rainbow" image.

I've tried to contact Olmatic through their website but they have not responded.

From what I've read, freezing at the rainbow screen usually indicates a current draw issue. I have the Raspberry Pi power source with 2.4 amps. The UPS also has a 300mAh LiPo battery. However the UPS does take some time to initially boot and begin providing power so there may be some fraction of time where the Pi is providing power to both hats. I don't know if the two hats would draw enough current from the Pi to cause the boot to freeze.
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Re: Ultimate GPS HAT

by adafruit_support_mike on Wed Apr 18, 2018 1:40 am

If the UPS Hat uses the GPIO Serial interface, you'd have two boards fighting to control the RasPi's RX pin. If one wants to pull the pin high while the other wants to pull it low, you could get something like a short circuit between the 3.3V and GND rails through the two boards.

That kind of thing is very likely to damage either or both boards, so verify the UPS Hat's pin connections before trying to use it stacked with the GPS Hat.

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