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How to use ENABLE pin in GPS Ultimate
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How to use ENABLE pin in GPS Ultimate

by 3dotter on Fri Jul 05, 2013 7:18 am

I find the pull up resistor remark on the Enable pin on your page:
http://learn.adafruit.com/adafruit-ulti ... ced-wiring confusing.
Is it not easier to have the Arduino to switch on the Ultimate GPS by turning
one of its digital PINs to HIGH after connecting this (power
on/off) PIN to the Enable PIN? And for Arduino use this code:

pinMode(powerpin, OUTPUT);
digitalWrite(powerpin, HIGH); // pull HIGH to turn on
digitalWrite(powerpin, LOW); // pull LOW to turn off

If this is possible, should there still be a 10 K resistor?

Or is this not possible? If not why? Perhaps then good to show a small
schematic of how it should be done for newbies like me.

Thanks in advance for responding.
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Re: How to use ENABLE pin in GPS Ultimate

by adafruit_support_bill on Fri Jul 05, 2013 9:00 am

Your code will still work. But the pullup resistor makes it high by default, so if you don't need to turn it off you don't need to do anything with the EN pin.

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Re: How to use ENABLE pin in GPS Ultimate

by 3dotter on Fri Jul 05, 2013 10:20 am

Thanks for your quick answer!

I need to switch it on and off. Just to make sure: do I need a (10 K) resistor or is a straight connection between my Arduino (power)PIN to the GPS' Enable PIN sufficient without a resistor? My Arduino has 3.3 V and I want the GPS also to work at 3.3 V.
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Re: How to use ENABLE pin in GPS Ultimate

by adafruit_support_bill on Fri Jul 05, 2013 10:45 am

The pullup resistor is built into the breakout board. You just connect directly to it. It will work with both 3.3v and 5v.

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Re: How to use ENABLE pin in GPS Ultimate

by ttapers on Mon May 02, 2016 5:51 pm

I've been playing around with the enable pin, connecting it directly to ground and off again manually with jumper wire, but I don't seem to see any change in GPS behavior. I would expect that the GPS should stop reporting an accurate fix when the enable pin is shorted with the ground pin, correct? Is there anything I'm missing here? Is there anything that's changed in the last couple years that may be causing this behavior?

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Re: How to use ENABLE pin in GPS Ultimate

by videoicu on Sun Aug 28, 2016 10:57 pm

Importantly, for us, grounding the enable pin on the GPS breakout does turn the GPS off but retains the RTC if there is Vcc connected to VBAT pin. I have a question though regarding power consumption. The spec on the GPS module itself says backup power consumption is 7uA at 3.3V. I have measured this and it is correct, looking at current though VBAT.

When I am looking at current through Vin, its normal at ~25mA while operating, but when I ground the ENABLE pin, it shuts down properly as expected, BUT the current is much, much more than just the VBAT draw and is more in the order of 400uA (.4mA).

Can someone explain why? I thought that by killing the GPS with ENABLE that current draw should drop to around the VBAT level of 7uA. Our design can not live (long) with a 400uA draw when sleeping.

Thanks for any input.

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Re: How to use ENABLE pin in GPS Ultimate

by franklin97355 on Mon Aug 29, 2016 2:04 pm

Check the schematic. Eagle files here There is a pull-up resistor from enable to vin that may be causing some of this. You could remove it and use the micro to make sure the enable stays high when you need it to..

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Re: How to use ENABLE pin in GPS Ultimate

by videoicu on Tue Aug 30, 2016 9:49 am

Franklin,

I think you were spot on with your response. I looked at the Adafruit schematic you referenced and also the regulator manufacturer's typical application schematic. They are showing exactly what you said. They pull down the ENABLE pin to ground with a 100k and use a GPIO HIGH to ENABLE the regulator and thus the GPS.

I will modify the breakout as suggested.

Thanks for leading me in the right direction!

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Re: How to use ENABLE pin in GPS Ultimate

by wrg_llc on Thu Feb 21, 2019 10:48 pm

I know this thread is old, but it's relevant for my question. Is it possible to modify the Ultimate GPS so that by default, e.g. when it's first powered up (connected to an Arduino) that it's disabled and won't draw power? Then only enabled by a GPIO pin, presumably going HIGH? This is useful for solar-powered project where you may need to recover from a completely dead battery under low-Sun conditions.

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Re: How to use ENABLE pin in GPS Ultimate

by franklin97355 on Thu Feb 21, 2019 11:12 pm

Check out the eagle files linked above to see where the resistor that keeps the GPS enabled is located and then remove it.

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