Using I/O pins

Author Message
Maniccyberdog
Newbie

Joined: 19/02/2018
Location: United Kingdom
Posts: 13
Posted: 01:23pm 11 Dec 2019      

Dear fellow MM users,

I'm just working on my first project and have a small problem (using a PIC32MX170).  I have a ILI9341 working ok, and a DS18B20 sensor all ok.  I'm adding a another sensor that gives a logic 0/1 at 3.3v but have been unable to get this to work.

So far I have tried 3 different pins 4,5,17

code used;
SETPIN 17,DIN
PRINT PIN(17)

I have also changed the option to pullup and pulldown both show the correct values with the print statement and nothing connected to the pin.  If I set the option to pullup and ground the pin, the resulting output is 1 from PRINT PIN(17)

What I'm I missing?
matherp
Guru

Joined: 11/12/2012
Location: United Kingdom
Posts: 11635
Posted: 03:06pm 11 Dec 2019      

Either you are not connected to pin 17 properly - check continuity, or you don't have a common ground. The pullup/down shows the pin is measuring properly
Maniccyberdog
Newbie

Joined: 19/02/2018
Location: United Kingdom
Posts: 13
Posted: 04:58pm 11 Dec 2019      

Grounds all good etc.  The  ds18b20 is ok and on the same ground
Turbo46

Guru

Joined: 24/12/2017
Location: Australia
Posts: 1694
Posted: 06:54pm 11 Dec 2019      

Are you using a backpack? Sorry but Matherp is correct. Unless you have a faulty chip - check continuity. Power down the unit, remove the display and use a multimeter to check continuity from the pin of the '170 to the connector. Maybe the IC pin is bent under?

Bill
Keep safe. Live long and prosper.
TassyJim

Guru

Joined: 07/08/2011
Location: Australia
Posts: 6546
Posted: 08:51pm 11 Dec 2019      

Check that your sensor is really going to zero volts.
If the zero reading works without the sensor connected but not when it is connected, your external sensor is holding the input too high.

Jim
VK7JH
MMedit
PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 669
Posted: 10:42pm 11 Dec 2019      

If you are getting this strange thing on pins 4,5 & 17 then it can't be a bent pin 17.
The common elements are your ground and software. Could there be something in your software?
Other than that, check the actual pin voltage as they are read.

Good luck

Peter
Turbo46

Guru

Joined: 24/12/2017
Location: Australia
Posts: 1694
Posted: 11:29pm 11 Dec 2019      

Sorry, ignore the bent pin idea. I didn't note that you had tried other pins.

If you are grounding the pin with your sensor and still reading a logic '1' on the pin, it could be that the 'ground' you are using is elevated above the true 0 volts. Maybe the sensor is drawing a lot of current through the ground? Have you disconnected the sensor and tried shorting to ground with a piece of wire or a clip lead. You may need to use a different ground point.

As others have said, check the logic '0' input when using the sensor with a meter - it should be less than 0.65v

Bill
Keep safe. Live long and prosper.
Quazee137

Guru

Joined: 07/08/2016
Location: United States
Posts: 603
Posted: 12:09am 12 Dec 2019      

You said you have a working DS18B20 on a different pin. Try it on the other pins
 and try the DS18B20 in question on the working pin.
Volhout
Guru

Joined: 05/03/2018
Location: Netherlands
Posts: 5994
Posted: 11:53am 12 Dec 2019      

In post #1 I read:

with internal pulldown enabled, the input pin reads 0
with internal pullup enabled, the input pin reads 1

with internal pullup enabled, and pin wired to ground, it reads 1

check the wire...

Volhout
PicomiteVGA PETSCII ROBOTS
bigmik

Guru

Joined: 20/06/2011
Location: Australia
Posts: 2981
Posted: 12:22pm 12 Dec 2019      

Hi Maniccyberdog,

What is the sensor you are trying to read?

It is possible that the sensor is either open collector or open drain?
Try a 4k7 resistor pulled to 3v3 .

Regards,

Mick
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
Maniccyberdog
Newbie

Joined: 19/02/2018
Location: United Kingdom
Posts: 13
Posted: 01:42pm 12 Dec 2019      

I found it!  I made a short cable between the sensor pin header on my own design backpack.  When a probe from my multi-meter was against it made perfect contact, I soon as I moved it away it was very intermittent. I guess thats what you get with parts from Ebay lol.

Thanks for all you help, loving my MM :-)
Turbo46

Guru

Joined: 24/12/2017
Location: Australia
Posts: 1694
Posted: 01:03am 13 Dec 2019      

That's good! Thank you for letting us know.

Bill
Keep safe. Live long and prosper.
PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 669
Posted: 01:33am 13 Dec 2019      

G'Day Manic & Bill

Good point Bill, It's nice to know when advice helps or in this case, he/she worked it out for him/her self.

Peter