6. Electronics design#
Group A (Thursday Session)#
” Group assignment ----
Use the test equipment in your lab to observe the operation of a microcontroller circuit board “
We used Digital Oscilloscope and Digital Multi Mater in fablab Kamakura.
Digital Oscillosope ( Tektronix TBS 1052B )#
Quick reference by Tektronix#
As shown in this reference, basic steps to use oscilloscope after “Making Connections” are ,,,,
Step1 : set the Vertical scale (Volt/division)
Step2 : set the Horizontal Scale (seconds/division)
Step3 : set the Trigger Type (Source and Levels)
Probe Compensation ( Calibration )#
One important thing in “Making Connections” is probe compensation.
In short, probe compensation is to adjust the capacitance of the probe ( + cable ) so that the wave form ( amplitude and/or response ) is properly shown on the monitor. When the probe was replaced, or after it was used with other oscilloscope, this probe compensation should be performed.
|connect the probe to “PROBE COMP”||5V, 1kHz square wave is observed.|
|If the wave form is deformed,,,||turn the small screw until the proper square wave is shown.|
wave observation ( Resonator )#
To check the most simple sine wave in the circuit, the output of the 20MHz resonator was checked.
|touch the resonator output with a pin (probe)||20MHz sine wave was observed.|
FFT ( Fast Fourier Transform )#
This equipment has FFT function which can analyze frequency distribution in the signal. In other words, this function converts the time-domain signal to the frequency-domain form. Practically, for example, in case that some kind of noise is observed in the signal, this could be used to identify where the noise comes from.
( although this video is using “signal analyzer”, this is a good explanation about time vs frequency domain.)
|1kHz square wave ( “PROBE COMP” signal )||push the FFT button, then the frequency distribution was displayed ( 1kHz, and other harmonics )|
I tried to check the signal from TX and RX pins using the oscilloscope. TX means transmitters which sends signal from laptop to the board and rx means receiver which sends signal backwards when it gets signal from the laptop.
setting slope as falling on oscilloscope
Now I can catch the signal from tx and rx.
character is controlled by Ascii code which is represented by hexadecimal. But in the serial communication, 8bit is used. It means 8 binary digits are used and need to change it to hexadecimal to read signals.
And signals comes as follows…
First 1 bit (0) is start bit which means the signal of the starting serial communication.
Then, 8 binary digits are sent but it coms as reverse order like from the last bit of 8 to the first bit of 8. last a few bits are stop bit which means the signal of the ending serial communication.
On echo program, I would send “o” from serial monitor on Arduino. It means signal of “o” go is sent via tx. Then, something could be return from the board (attiny44).
[the signal of TX]
6F means “o” in Ascii code
so that’s same as I inputed from Arduino’s serial monitor.
and, 0A means LF in Ascii code = NewLine (the end)
LF is always sent at the end of the signal.
[the signal of RX]
68 means “h” in Ascii code
It is because the echo hello 44 board returned as follows
Using a digital multimeter(Tsuchiyama)#
Digital Multimeters (DMMs) are general-purpose measuring instruments that combine basic measurement functions such as voltage, current, and resistance in a single unit and are used in all aspects of electrical measurements.
The DMM is particularly superior to conventional indicating instruments and analog testers in the following ways.
- High accuracy and resolution thanks to advances in A-D conversion technology.
- Digital values are displayed using an A-D converter and there is no reading error.
- Input resistance is high (>10MΩ at DC voltage and >1MΩ at AC voltage), so it does not affect the object of measurement and can be considered as ∞Ω for most measurements.
- The input terminals are isolated from the power supply and interface to ensure safety and accuracy of the device under test.
A digital tester, like an analog tester, applies the test pins of the test leads to the measurement site for measuring voltage and current.
The voltage and current taken out of the test pins are sent to the LSI centering on the AD converter and the peripheral circuits through the switch circuit switched by the switch knob.
The values processed by the LSI are displayed on the display unit as numbers and symbols.
In the resistance measurement, a current is passed through the test leads, which are switched by the switch knob, to the resistor to be measured, and the processed voltage is fed to the LSI.
The value processed by the LSI is displayed on the display unit as a number or symbol.
A feature of the digital tester is that the measured value is displayed as a number, so there is no reading error.
Group B (Saturday Session)#
I would like to review how to use digital multimeter.
Measure the AC voltage.
Measures DC voltage.
Measures DC voltage in mv.
Measure the resistance.
By pressing the yellow button with the resistance mark, you can measure the capacitance of the capacitor.
Testing for continuity
perform a continuity test on the diode. A liquid crystal display called V appears.
It is convenient to check the polarity direction of the anode and cathode.
Measure the current by adjusting the rotation to the mA position.
Adjust the rotation to the position of A, plug the plug into 10A and measure the current.
Note that if you measure the voltage in the current measurement mode, the fuse in the tester will blow.
The current of the “echo hello-world board” created this time was 0.24mA.
When the voltage was measured, it was 4.923V.
The rated voltage of the PC is 5V, but the measured value has an error of about 5% before and after depending on the tester.
How to use an oscilloscope
Oscilloscope is a device used to test the functionality of equipment that generates an electrical signal. Oscilloscope measures the voltage or current of an electrical signal over time, and display the signal as a waveform in a graph.
We used Tektronix TBS1052B.
The main specifications are below;
|Vertical Resolution||8 bits|
|Band Width||50 MHz|
|Sampling Rate||2.0 GS/s|
I’ll explain how to use an oscilloscope.
① Vertical Control
Position, Show & Hide, Scale (per division)
② Horizontal Control
Position, Scale (per division)
Decide the threshold to catch and capture voltage waveforms and its location.
This time, we use Slope trigger. Slope is set as Rasing or Falling. Rasing sets the threshold to the rasing of the signal and Falling sets it to the falling of the signal.
Inserting probes into it, you can measure and show several waveforms at the same time.
⑤ Probe configuration
⑥ Run/Stop and Signal
When Run/Stop is on, oscilloscope continues to record signals to its memory. It is used when you’d like to measure the steady voltage or current.
When Signal is on, oscilloscope capture signals at certain threshold you set at Trigger function. It’s like camera.
Next, The monitor side.
① Each button corresponds to the icon at right side of the screen.
② You can select the icon by rotate the dial.
Other functions are FFT. FFT (Fast Fourier Transform) is the waveform transfer technique that transfer the waveform over time into that over frequency and re-transfer it. You can use it when you’d like to find the cause of noise in the signal. It will decompose the signal waveform over time into frequency components and you’ll find the noise-related frequency in it.
Notes that the waveform over time is the superposition of waves which has an inherent frequency.
We used oscilloscope to decipher the signals sent into and sent out of the board.
A ground line was soldered onto the board. We connected both the 2 GND clips to the ground line. Yellow clip was clipped to Rx (the one that receives signals) and blue to Tx (the one that sends out signals).
Once inputting a letter into serial monitor, ocilloscope shows the wave of the signals.
We set the trigger to “Slope - Rising”, and enlarged the horizontal axis to see the waves clearly.
The image below shows the starting of the waves.
The waves represents 0 and 1 in binary number system.
One bit represents one number, so the blue wave represents 00101111010010100001.
10 bits represents 1 code.
The 1st bit is always 0, representing start, and the 10th bit is always 1, representing the end.
The 8 bits in between are listed reversely, so it is actually 01111010.
The 8 bits are broken down into two 4 bits. Each 4 bits represents 1 letter in hex.
0111 is 7, 1010 is A.
In ASCII code, 7A represents z (see ASCII code table). So we can see from the waves that we input “z”.
In the same manner, we can read that the following 10 digits “0010100001” represents “New Line”.
This verifies that we input “z” and “Enter” correctly into the board through serial monitor.