Current meter is burning out microcontroller

[walters]

When measuring the current out of the battery power supply

The microcontroller has 4 different states before going to sleep

It will start at 50ma then to 20ma, then to 5ma, then to 1 ma then the microcontroller will go to sleep at 10uA

When measuring the current using a DVM it really trips out the micro-controller and burns out the chip or certain inputs and outputs
Why?

What is the reason why measure current using a DVM is bad for microcontrollers and does a DVM in series adds a LOAD ( meter loading problem? ) to the circuit?

 

[tpetar]

I didnt hear for this, I've never seen it. :shock:

Please describe what uC and what DVM you use. 8-O

---------- Post added at 05:06 ---------- Previous post was at 03:55 ----------

Maybe try to use high impedance dvm.

 

[skylarks]

Micro-controller uses adc to read the voltage drop across the current sensing resistor and this voltage drop should not increase from supply volt of the controller. If DVM has loose connection or high resistane then the voltage going to adc would be higher enough to damage the controller. you should not detach the current sensing circuitry of the controller and then use DVM in series.
hope it will help you.

 

[ahsan_i_h]

May be proper power supply bypass capasitor is absent in the circuit.

 

[walters]

Micro-controller uses adc to read the voltage drop across the current sensing resistor and this voltage drop should not increase from supply volt of the controller. If DVM has loose connection or high resistane then the voltage going to adc would be higher enough to damage the controller. you should not detach the current sensing circuitry of the controller and then use DVM in series.

Block Diagram:

Battery's 4.5 volts to DVM Current meter to current sensing circuit to micro-controllers inputs


It's either tripping out the current sensing resistor or circuit

Or It's tripping out the V+ voltage of the micro-controller, sense the battery volts go to V+ to the micro controller

May be proper power supply bypass capasitor is absent in the circuit.

If this power supply bypass capacitor is not in the circuit what will it do to the microcontrollers input or V+ input

 

[ahsan_i_h]

Block Diagram:

Battery's 4.5 volts to DVM Current meter to current sensing circuit to micro-controllers inputs


It's either tripping out the current sensing resistor or circuit

Or It's tripping out the V+ voltage of the micro-controller, sense the battery volts go to V+ to the micro controller



If this power supply bypass capacitor is not in the circuit what will it do to the microcontrollers input or V+ input

If the proper power supply bypass capasitor is not present in the circuit, then the lead inductance of the DVM will cause trouble. When the uC will try to switch on any load, then the voltage drop in the lead inductance will cause voltage dip and will cause restart problem. Again if any high value capacitor is connected to any of the input, then that capasitor will try to get dischared to low voltage power supply through input protection diode and will cause SCR latchup problem. SCR latchup will burn your uC.

 

[walters]

What the Micro-controller has been doing is having problems is the booting up and then it causes the display to either flash and trying to boot up and then it will fry the display, so i have to change the displays a lot. Or it will burn out the micro-controller

Where do I put a series resistor after the DVM meter? or bypass Capacitor

Don't I need also protection diodes for the micro-controller?

 

[dselec]

How can we reply without a circuit ?

 

[walters]

Disconnect the + terminal of the battery from the device.
Put the multimeter in current measuring mode.
Connect the red lead on the multimeter to the + terminal of the battery.
Connect the black lead on the multimeter to the + lead from the device.

This Is what I am doing and it is frying the microcontroller and display

Is it causing the micro controller to have boot up problems, screen is flashing and burns out the micro controller or display

I am measuring the Current from the battery to the DEVICE or circuit

The circuit/device is not happy with putting a DVM meter inbetween the Battery and to the circuit/device

It frys the micro controller and display

Block diagram:

Batterys----- DVM in current mode--------Circuit

 

[dselec]

HELLO THERE r u tryng to measure current to the circuit , the u cant use some digital current meter in series with supply supplying current to circuit, u need to do current sensing.
sooory but its just stu.... ok ok i will not use un polite words.

 

[walters]

We just measuring the resistance of the Fluke DVM meter set to current mode in the mA range it was a resistance value and the uA range had a resistance value

Have you tried this on your guys meters?

Measure the resistance of your DVM meter set in in the mA range and to the uA range and what do you guys get?

 

[dselec]

resistance of the Fluke DVM
its in the fluke manual.

 

[walters]

I just measured again the Fluke meter with another Meter

The milliamp Range = 1.5 ohms
The microamp Range = 100ohms

What resistor value can I use so i can measure the voltage instead of use the current meter?

The Tech at my work said the current meter is a voltage divider because it is in series but it is connecting to the input of the power supply circuit but at the beginning it has a resistor that does to ground.

So the meter is loading or changing the power supply input , input loading problem

But What value can i use please? because it has to go down to 10uA of current and up to 55mA of current

Not sure what value of series resistor i should use?

 

[dselec]

Hello......
We cant go on like this post .your circuit diagram or draw it and post .
Its just stupid and wast of time guessing what u are really doing.
and 100 ohm is bad for your circuit, and connecting fluke to a between batt supply to mpu is unresponsible u dont know/understand how the internal fluke circuit works so STOP CONNECTING FLUKE IN SERIES TO MPU.....STOP...STOP...
And more any body else understand his circuit and post for him.