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Multi-meter connection to the ground and interruption

 
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qwwe



Joined: 17 Sep 2017
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Multi-meter connection to the ground and interruption
PostPosted: Mon Feb 26, 2018 8:08 am     Reply with quote

Hello
I closed a circuit that works fine. In this circuit, I used an external interrupt, and from three a/d channels microcontroller pic16f1829. And the display used is the Nokia 5110. For that, I used the library in the link below. Initially, the circuit got a little noise that was solved by adding a RC filter to the input of the analog to digital converter.

http://www.magusporta.com/tips/nokia_driver/nokia_driver.html

But now I'm having a problem while testing the circuit. When a negative multimeter is connected to the circuit board near the microcontroller, the interruption occurs or the display becomes clear and does not display anything and does not indicate anything, of course it does not turn off. As long as I reset the circuit. It is very weird. This problem also occurs by connecting the positive base of the multi-meter to the interrupter base. Of course, for other parts of the circuit, this is not the case, and this problem occurs only when I close the microcontroller or interrupt pin. Is it in a multi-meter orbit that affects microcircuits. I tested two multimeters, both of which were the same. Or a programming bug. I've closed the circuit on a few breadboards, and of course I've used high wires and I've used an 8 MHz internal microcontroller oscillator. Sometimes the output will change somewhat by touching the amplifier ground that amplifies the signal. I'm really confused. What can be the problem?
temtronic



Joined: 01 Jul 2010
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Location: Greensville,Ontario

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PostPosted: Mon Feb 26, 2018 8:39 am     Reply with quote

This is without seeing a picture of your setup, but it sounds like your project is not connected to 'Mother Earth', ie properly grounded and so any wire you attach to it is an 'antenna', picking up stray energy and getting into the PIC.
qwwe



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PostPosted: Mon Feb 26, 2018 1:06 pm     Reply with quote

I connected all the grounds in the circuit and tried to connect all to one point. My circuit is connected to a 5 volt power supply, and then using the regulators lm2576 and ams1117 3.3 V and 2 voltages I made 5 volts for different parts of the circuit. All of them are connected together.
Please explain a bit more about the "mother earth".
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Mon Feb 26, 2018 1:44 pm     Reply with quote

There are many reasons for this.

1. Poor board layout.
2. Incorrect MCLR circuit.
3. Floating unused pins on the PIC.
4. Lack of bypass capacitors on the PIC, or incorrect placement,
or incorrect capacitor values, or incorrect types.
There are a lot more reasons than just this.

This 3-page thread has a critique of a board layout. The photos are are
still there. You should study this 3-page thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=52859

More tips on board layout.
http://www.ccsinfo.com/forum/viewtopic.php?t=34352
PCM programmer



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PostPosted: Mon Feb 26, 2018 1:46 pm     Reply with quote

temtronic,
A lot of the people on this forum are not from the Anglo cultural world.
They don't understand the idioms or cultural references. It just creates
confusion if you use them.
Ttelmah



Joined: 11 Mar 2010
Posts: 13788

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PostPosted: Mon Feb 26, 2018 1:58 pm     Reply with quote

There is an extra point because of the supply that is being used.
The 2576, is a great switcher, but needs very careful layout of the section between the chip, inductor & switching diode. If there is less than optimal layout here it can be prone to massive oscillation. A tiny change introduced by a multi-meter lead is just the sort of signal that can trigger this. National do a very detailed application note about the layout needed.
The AMS1117, also requires a capacitor of a very specific ESR placed close to the regulator, or it too can be prone to oscillation.
temtronic



Joined: 01 Jul 2010
Posts: 6332
Location: Greensville,Ontario

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PostPosted: Mon Feb 26, 2018 2:11 pm     Reply with quote

yes, I tend to forget 'stuff' that comes natural to me....sigh, 65 this year...
'Mother Earth' means that the ground of your product is connected to the electrical ground of your house which is supposed to be connected to a 'ground rod', a copper clad bar, 2 Meters long driven into the ground just outside your house.
Without this connection , your project is 'floating' and is more suseptable to airborn electrical noise. You play a part in this 'antenna' as well as you may be touching the DVM wire ,making a bigger antenna, which sends more noise to your project
As both PCM P and Mr. T point out, board layout for switching power supplies has to be correctly done, proper capacitors are important, unused inputs need to be either pulled high or low as well.
Getting to the source of the problem can be time consuming, so make a check list and try one item, if it doesn't work, check it off and then try the next item. This way you don't have to second guess, 'did I already do that ?'
Having an oscilloscope is a 'must have' tool these days as it allows you to SEE the actual signals.

Jay
qwwe



Joined: 17 Sep 2017
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PostPosted: Tue Feb 27, 2018 12:24 am     Reply with quote

Thank you for your answer.
I used digital ICs such as lm75, pic16f1829 and cd4066, analogs like the ad8572 and lm385, from the capacitance 0.1uf for the direction of the vcc to the ground.

I'm currently closing the circuit breadboard.
But I have not designed it for pcb yet.
I use a resistor attached to the VCC for the MCLR pin and a key that connects the MCLR pin when resetting to the ground, which works correctly.
I used all microcontroller pins in this circuit and no pins are floating.
For this circuit, it only happens that the negative ground of the multimeter is connected to the ground near the microcontroller.

Of course, the microcontroller output pin I used to control the CD4066 keys does not have to be connected to the pull down resistor OR pull up resistor because they should be sometimes zero in the program and sometimes one. Namely their software is sometimes set to zero, and sometimes one and never is defined float.

I just pull up OR pull down the input pins in the form of hardware with the key and the resistance.

I used a 100UH inductor and an SS34 diode and an input capacitor of 100UF and a 1000UF output capacitor for the LM2576, and I used a 10UF input capacitor Electrolytic and Two parallel 10uf output capacitors Electrolytic for the AMS1117.


digital grounds is connected to each other and analogue grounds are connected to each other.Then I've connected them to the main source ground. I have connected the digital grounds using the ferrite bead to the main source ground.
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