Group Assignment – Electronics Design - CDMX
General objective (group assignment):
- Use the test equipment in your lab to observe the operation of a microcontroller circuit board
Oscillometer
Technical characteristics
- Model: UTD-4000
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Working specs:
- Input: DC, AC, GND
- Maximum input voltage: 400 V
- Time delay between channels: 150 ps
- Sampling modes: Real-time
- Acquisition rates: 2 GS/s (two channels: 1 GS/s)
Multimeter
Technical characteristics
• Model: UT-800
• Working specs:
o DC Voltage : 6 V / 60 V / 600 V / 1000 V / 2000 V
o AC Voltage : 6 V / 60 V / 600 V / 1000 V / 2000 V
o Variable frequency voltage : 600 V
o Frequency : 10 Hz – 10 kHz
o Resistance : 600 Ω / 6 kΩ / 6 MΩ / 60 MΩ
o Capacitance : 60 nF / 600 nF ~ 600 μF / 6000 μF / 60mF
Development
Our work will be to describe and understand the parameters to expect during a correct operation of a microcontroller. This is important, because with this, we will detect if the microcontroller has failed or if there is a physical problem in our boards. The assignment will be divided in two parts: checking the operating voltage and the oscilloscope tests.
Operating Voltage:
Our boards will be working with different voltages for the items we will be connecting, the microprocessor needs a 3.3 V current, many sensors use 5 V, and if we are using motors, we will be needing anything between 12 and 24 V. These differences can be measured along the routes with the multimeter, assuring that each component is receiving a voltage within it’s operating range.
To make this we will be using our multimeter:
- Connect the board to the current (our board uses a USB pin to get 5 V and an external converter to get 12 V).
- Set the multimeter to the voltmeter mode.
- Touch with the black end the GND route of your board.
- Touch with the red end the route where you want to measure voltage.
This will show in your multimeter display the electric current present in that part of your board.
The second function we tested was continuity, this will allow you to understand if any part of your board is working incorrectly because it is not connected to the circuit you want or vice versa, to do this you need to:
- Unplug the board and allow all capacitors to discharge to ensure a correct reading.
- Set the multimeter to the Resistance/Continuity/Diode position and change the function with the button.
- Touch with both ends the same circuit, if there is a resistance lower than 10 ohms, the multimeter with emit a beeping sound. That is the signal that your circuit has continuity.
There are other ways to use the multimeter, such as checking the correct polarity of a connected circuit or a diode.
Oscilloscope tests:
Nevertheless, not every problem can be detected by measuring voltage or continuity, we have to know what the signal looks like. To do this, we will be using an oscilloscope.
This oscilloscope has to be connected to both sides of the circuit (current and GND) and it will show us the waveform of the electronic signal in a graph. The importance of this measurement is that we can make an interpretation of what is the microprocessor doing or if it is sending the same signal that we asked it to (in time and strength).
We made some tests to compare the way two different microprocessors send the signals to our stepper motor.
We compared an ATTiny 84 (yellow line) and a SAMD11C (blue line):
This were the result we got:
We compared an ATTiny 84 (yellow line) and a SAMD11C (blue line):
This were the result we got:
The graphics we observed demonstrated how both microprocessors work differently. The SAMD11C worked by sending a steady pulse for a period of time and stop to once again send the pulse. The pulse looked steady in both moments, High and Low. The ATTiny emitted the pulse and did not sustain the strength and just lets it fall down to -1.