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Lissajous Patterns on an Oscilloscope using Silego GreenPAK4 Development Kit and SLG46620V

Lissajous Patterns on an Oscilloscope using Silego GreenPAK4 Development Kit and SLG46620V

lissajous 2 to 5 ratioIntroduction
What are Lissajous Patterns?
Lissajous Patterns are the result of two sine waves controlling the X and Y axes of an oscilloscope.
Lots of science fiction movies will show Lissajous Patterns on oscilloscopes as it is a very impressive thing to display.
https://en.wikipedia.org/wiki/Lissajous_curve
What is an Oscilloscope?
An oscilloscope is an electronic device used for viewing waveforms or electronic signals on a screen.
https://en.wikipedia.org/wiki/Oscilloscope
What is a Silego GreenPAK4?
GreenPAK4 is a highly versatile NVM Programmable Mixed-signal Matrix designed to easily implement differentiating features and functions into already highly integrated designs while minimizing component count, board space, and power consumption. GreenPAK4 comprises the best analog and digital resources from previous generations with expanded functionality and a few new additions, such as the hardware reset pin and Digital to Analog Converter (DAC), all in a tiny package.

Prerequisites
Oscilloscope and test probes
I use a Philips PM3217 which has served me well for many years
Silego GreenPAK4 Development Kit and SLG46620V
STQFN-20 (2.0 x 3.0 mm) GreenPAK4 Dual Supply Socket Adapter
Silego GreenPAK4 Designer
http://www.silego.com/products/greenpak4.html
Tweezers with antistatic coating and needle tips

Warning
As with most electronic parts the Silego GreenPAK4 Development Kit and SLG46620V are sensitive to static electricity. Ensure all static precautions are taken while using the board to prevent damage.

Setting up the board
Rather than permanently programming the SLG46620V we will be using the emulator function in the GreenPAK4 Designer software. Although the software calls itself an emulator it will actually be running on the IC. Using the emulator means that we will be able to program the IC (or use it in the emulator) again in the future, and more importantly for this tutorial we can change figures on the fly to generate different patterns and not have to burn a single use IC in the process.

I suggest working in a clean, uncluttered area with a sheet of blank white paper to put the board on while you are doing the initial set up. The IC we will be using is tiny, measuring 2 millimetres by 3 millimetres and will easily get lost forever should it drop onto a dark surface.

boardRemove all connections from the development board (including USB and the socket adapter).

socket openPlace the STQFN-20 (2.0 x 3.0 mm) GreenPAK4 Dual Supply Socket Adapter on your work area and open the top by pulling the tab slightly away from the socket adapter which releases the top panel revealing a tiny hole to carefully place the IC.

If you examine the IC you will see that one side has silver pads and the other has text. The side with the text is the top and has a small dot on one corner. This dot is the orientation point.

If you examine the socket adapter with the top panel open you will see a dot. This dot is also an orientation point.

Using your tweezers, pick up the IC, taking note of the orientation point. Place it carefully into the hole in the socket adapter ensuring the two orientation points are together and the text is still on top. Be extremely careful not to damage the pins inside the socket adapter or it will be permanently damaged and require replacement.

Once the IC is aligned and seated correctly open the tweezers and remove them before reclosing the top panel on the socket adapter.

board and socketNow connect the socket adapter to the larger board using the pins in the centre of the board, paying particular attention to the pin alignment.

Finally insert the USB cable into the USB port.

Installing the software
The software can be downloaded from http://www.silego.com/products/greenpak4.html. There are versions for Windows, Mac and Linux. I will be using the Linux version. Please follow the instructions for your particular system.

set chip revision windowOnce installed, run the software. A window will open asking you to select your GreenPAK4 chip revision. We will be working with the SLG46620V so select that one.

When the software has finished loading click on the Emulator button or press F9 on your keyboard.
emulator 1A new (rather curvy) window should open with the message “Please connect device to USB port”. Follow the instructions and plug in the USB cable. Sometimes I get an error message “The critical error message detected…” but I ignore it and click OK.
If you look at the bottom right corner of the window it says Chip P/N SLG46620V. This message means the computer can see the IC and all is well with the board.

emulator Signal Generator menuUse the secondary (right) mouse button to click on the box labelled TP3 and a new context menu will open. Select “Signal Generator”. Repeat this step for the box labelled TP6.

Setting up the oscilloscope
Each oscilloscope is different but basically we will be taking two probes and connecting them to the first and second ports of the oscilloscope and having one probe control the X axis and the other control the Y axis.

We will be using pins 3 and 6 of the GreenPAK4 board. I have arbitrarily selected those pins to allow clearance for the oscilloscope probes. The only requirement is that the pin is not VDD or GND and that it can be configured as “Signal Generator”.

Your test probes should come with crocodile clips that connect to GND. Connect those to one of the two rows of 6 pins sticking out of the board. Both sets of pins are marked GND.

TP3 TP6Take the probe connected to the X axis of the oscilloscope and connect it to the white connector on the board marked TP3. Take the other probe and connect it to TP6. You should now have 4 connections from the oscilloscope – 2 probes connected to TP3 and TP6 and 2 crocodile clips connected to GND.

Creating the Lissajous patterns
Signal Wizard windowWe will generate two separate sine waves, one on each pin TP3 and TP6. When they are displayed on an oscilloscope screen they interfere with each other in interesting ways.

Using the main mouse button double click on the box labelled TP3 at which point a new window will open. This is the Signal Wizard window.
The Signal Wizard window can be divided into two parts:
The signal generator settings on the left and the signal display on the right.

If you look to the right (the signal display) you will see three graphs. The top is VDD and should not be altered under any circumstances. The middle graph is TP3 and the bottom graph is TP6.

Signal Wizard window smallClick on the middle graph (TP3) and make the following changes to the Signal Generator settings:
Type: Change from “Const. Voltage” to “Sine”
Amplitude: Change from “2750.6 mV” to “1650 mV”
Zero offset: Change from “2750.6 mV” to “1650 mV”
Period: Change from “1000 ms” to “30ms”
Double check all the settings and click “Apply”

Click on the bottom graph (TP6) and make the following changes to the Signal Generator settings:
Phase: Change from “0” to “3Pi/2”
Type: Change from “Const. Voltage” to “Sine”
Amplitude: Change from “2750.6 mV” to “1650 mV”
Zero offset: Change from “2750.6 mV” to “1650 mV”
Period: Change from “1000 ms” to “45ms”
Double check all the settings and click “Apply”

Nothing will change on the oscilloscope, this is expected.

Do not close the Signal Display window as we will be making changes shortly.

Emulation Active smallSwitch back to the Emulation window and click on “Emulation” on the right hand side. The “Emulation” and “Test mode” buttons will change colour to orange. Switch back to the Signal Display window and look at the bottom.

Signal Wizard Start Pause StopThere is a radio button marked “All” and three buttons marked “Start”, “Pause” and “Stop” respectively.
Click on “All” so the radio box is filled and then click on “Start”.

Oscilloscope CircleThe oscilloscope screen should now show a circle.
If you see an oval you can use the controls on the oscillator to make it the correct position and size.

On my oscilloscope the settings are:
A/Alt/Chop/Add/B: B
AC/DC/DTB/MTB/X Defl/AC/AUTO/DC: X Defl
A Position: Unused
B Position: Used to control Y (vertical) axis
Delay Time: 0:0
Level/Slope: Unused
X Pos: Used to control X (horizontal) axis
Ampl/Div: 0.5v
Time/Div: Off
Hold off: Unused
Trace Sep: Unused
AC/DC: DC
O: Off
Del’d TB: All off
Main TB: A

Once your oscilloscope is correctly showing a circle in the centre of the display we do not need to change any settings.

Lissajous 1We can now generate some Lissajous patterns.
To do this switch to the Signal Wizard window and click on the TP6 graph.

Lissajous patterns are created when there is a difference between the period of two sine waves. By adjusting the Period setting for TP6 we can generate our first one.
Change Period for TP6 to 15ms and click Apply.
This will give you a shape resembling a curved V. Not very exciting is it?
Let’s see it move then.
Change Period for TP6 to 15.10 ms and click Apply.
The lissajous figure will now be rotating.

By making a slight difference to Period we can control the speed of rotation.

Decent figures for TP6 can be found by using TP3/n where n is a whole number eg 2, 3, 4 et cetera.
For example TP6 = TP3/3 = 30/3 = 10ms gives a 3 pointed Lissajous pattern.
To see it move set TP6 to 10.1

After a while you will doubtless get frustrated with clicking “Apply” after every change. If you click on the box next to “Auto Apply” then changes are made simply by pressing the Enter key.

One of my favourite values for TP6 would be 30.1 ms, which is a slowly rotating circle. Make it faster by changing TP6 to 30.3 ms.

Go ahead and impress the people around you. At work use it to convince management you need a bunch of new tech toys, your wife that your kit is actually useful and your children that you are the cleverest person they know.

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