PSoC I2C Address Scanner (I2C Scan)

Introduction 
This short post covers a change to a PSoC Creator project created by Bob Marlow (Infineon Developer Community) for scanning an I2C bus.

Reason for the Updated Project
While experiencing issues when communicating with a Midas I2C display (MC20805A6W-FPTLWI-V2), the I2C address needed confirmation. Upon testing with a PSoC project (I2CScan) authored by Bob Marlow, the PSoC program did not output a response to the terminal program with an I2C address even though the Midas display was connected correctly to the PSoC. This was curious because the display was newly purchased.

Test Setup - PSoC Development Board with Midas I2C Display

Narrowing the I2C Address Range
Using two hardware connections on the Midas display, the I2C address can be configured for various I2C address options. For testing, the range of the variable I2CAddress in the PSoC code was limited from 0x3A to 0x3F. A short delay (padding between transmissions) was added to the code to make debugging on an oscilloscope easier.

Status = I2C_I2CMasterSendStart(Address,I2C_I2C_READ_XFER_MODE);   

The Midas display did not respond to the read command shown above. However, after changing the code to use the I2C write command, the display responded with its expected address.

Status = I2C_I2CMasterSendStart(Address,I2C_I2C_WRITE_XFER_MODE);

Tera Term - Midas I2C Address

The captures below illustrates the I2C replies, when the 0x3F address was used with the read and write transfer modes for the PSoC function I2C_I2CMasterSendStart.

Midas Display - NACK to Read I2C Packet

The ninth bit (left MSB bit first) in the SCL clock train (yellow trace) in the above trace shows that the corresponding position in the SDA trace (blue trace) was high and therefore represents a negative acknowledgement (NACK) to the read command; the same bit position on the trace below has a low on the ninth bit (blue trace) represents an acknowledgement (ACK) to a write command.

Midas Display - ACK to Write I2C Packet

For further information, see Figures 6 and 7 in the TI document ‘Understanding the I2C Bus’ for waveforms relating to I2C ACK and NACK responses.

Code Changes
The code change mentioned in the above paragraph was implemented in the PSoC TestI2CAddress function located in 'main.c'. Other changes were made in main to suit the terminal program TeraTerm.

Testing Other Devices
To ensure the code change would work with other devices, two other I2C devices were tested; an Adafruit SI1145 light sensor and an INA219 current sensor. 

Test Setup - PSoC Development Board with SI1145 Sensor

Tera Term - I2C Address from SI1145 Sensor

 

 

Test Setup - PSoC Development Board with INA219 Sensor

Tera Term - I2C Address from INA219 Sensor

Downloads and Disclaimer
The updated PSoC Creator project v1.1, for a PSoC4 device, can be downloaded as linked below. The original project is copyrighted and remains the property of Jörg Meier Software as noted in the project source.

I2CScan-v1_1.cywrk.Archive01.zip

PCB Artwork - Coaster (Dark Chocolate Imprint)

Introduction 
In this blog, the circuit board tool Altium Designer was used to create a circuit board (PCB) coaster with an imprint on the PCB resembling a dark chocolate (cocoa) molecule.

Prototype (Coffee) Cup Coasters

Finding a Suitable Source
Before the PCB design process could be started, a suitable molecule for the PCB imprint was found online. A representation of a molecule that was more uniformly shaped was chosen to suit the shape of the PCB. Such a specific layout may not be available without manipulating the molecule’s layout.

Dark Chocolate Molecule
(Courtesy biobeat.nigms.nih.gov)

The molecule in this post could have been caffeine, tea or several water molecules however for this post dark chocolate was chosen.

Creating the PCB
To begin creating the PCB artwork for the coaster in Altium, a circular arc on mechanical layer 1, with a 90 mm diameter was drawn. The 80 mm PCB diameter used in the previous coffee cup coaster was marginally too small however the overall PCB dimension should be adjusted on a project-by-project basis.

Coaster PCB Shape and Size

Next, the names of the individual chemicals were added as top copper layer strings. The font type sans serif was selected over serif for a modern appearance. Then the bonds between the chemical text were added to the PCB on the top overlay. Various placement and shuffling of top overlay line lengths and text were needed.

Coaster Top and Silk Layers

The next step was to duplicate the top copper layer strings. The layer properties of the copied strings were changed to the mechanical top solder layer and then placed over the top layer strings. This effectively removed the top solder mask exposing the PCB copper. Having a separate top solder layer allows for manipulation of the size and placement.

Coaster Top Solder and Silk Layers

Viewing the PCB using the Altium 3D feature yields the image below for the black solder mask.

Coaster in 3D

PCB Export
The requirements of the desired PCB manufacturer were checked to prepare the PCB artwork for manufacturing. As the files for the PCB manufacturer are usually in the Gerber format, the export settings for the Gerbers should be verified with the manufacturer.

Manufacturing
As noted in other blogs, the appearance and cost of the manufactured PCB may vary based on Production settings. For the PCB in this post, a black solder mask is more expensive than a green solder mask, the latter being more common.

In this post, the PCB thickness was kept at 1.6 mm since this is usually the most cost-effective thickness, a lead-free HASL (Hot Air Solder Levelled) surface finish was chosen over a lead finish and the solder mask was produced in two separate colours, green and black, to exhibit the visual difference. Lastly, the PCB manufacturer's marking was specified on the PCB bottom side overlay.

Downloads
The Gerber file can be downloaded from the link below. The files should be checked before use.

For the Gerbers the Altium export settings here were followed.

Coaster Gerber Files

TDR Pulse Generator (Microchip)

Introduction 
This post continues a previous blog that used a microcontroller driver design to generate a fast-rising edge for educational and bench-testing purposes. The microcontroller (PSoC) in the earlier blog was replaced with a microcontroller from Microchip (ATmega16U2). The board uses the Microchip part and is powered by USB.

Pulse Generator PCB

Why Another Generator
While the previous design using a PSoC microcontroller was received well, the price of a PSoC microcontroller has become twice that of a competing device such as the Microchip ATmega16U2. Consequently, a design was produced to utilise the Microchip microcontroller.

Circuit Board Design
As featured in the previous design, a pulse train is initiated from a microcontroller (ATmega16U2).

ATmega 16U2 for Pulse Generation

The same output driver arrangement was reused on this design however the output driver was changed to a Nexperia 74AHC04 because of the 5 V supply rail (USB). A linear regulator was considered to maintain the supply rails at 3.3 V but was ultimately not included to keep the total cost as low as possible. Five outputs of the 74AHC04 driver are still connected in parallel to individual 249 R resistors. All five outputs are tied together thus providing a calculated 49.8 R at the output, CN2.

Buffered Output for Pulse Generator

Software Design for Output Pulsing
A minimal software (code) project was prepared in Microchip Studio. This application generates a pulse by direct and continuous writes to the microcontroller port. The code to generate the pulses is shown below.

int main(void)
{
	DDRD = 0x08;
	PORTD = 0x00;
	for (;;)
	{
		PORTD |= _BV(PD3);
		PORTD &= ~(_BV(PD3));
	}
}

USB hardware connections were made to the ATmega to allow developers or users to enhance the code further. The ATmega software could be developed to support USB-controlled commands. Below are some links for software that may allow for HID solutions with the USB.

https://github.com/NicoHood/HoodLoader2

https://gitlab.com/arksine.code/HID/-/tree/2.0

A Note on Programming
The post includes details regarding the programming of the Microchip part because this design is intended for the educational system or illustrative purposes.

The 6-way programming connector on the pulse board interfaces with the ATmega. The connections are designed for SPI programming. See Table 3-6 in the Atmel ICE document for information concerning connections between the programmer and Microchip microcontrollers.

SPI Connector Pinouts

For programming of the microcontroller in this blog, the ‘Atmel squid’ connections were made to the pulse generator board as shown below.

SPI 'Squid' to Pulser Board

PCB pad jumper J1 should be shorted with solder to power the external oscillator.

Powering External Oscillator J1

The settings displayed below are taken from the Microchip Studio's, Tools menu, and the Device Programming item. The settings can be adapted based on the functionality needed on the board. For example, the onboard 8 MHz oscillator could be replaced with a different frequency device or the board could be redesigned to suit a crystal.

Microchip Studio ISP Clock Settings

Microchip Studio Oscillator Settings

 

Microchip Studio Fuse Settings

Microchip Studio Fuse Settings Continued

Testing the Board
Since the output driver voltage rails were changed from 3.3 V to 5 V, the output rise time (10% - 90%) was predicted to be slower.

Prototype Pulser PCA

Drive Voltage from Pulse Tester (Microchip)

 

Period from Pulse Tester (Microchip)

Signal measurements were again performed on a Keysight oscilloscope with a 20 GSa/s resolution. This board showed a rise time of 1.11 ns when measuring for a rise time of 10% to 90%.

Output Waveform Rise Time from Pulse Tester

Reflectometry Testing
Reflectometry tests were performed with a benchtop oscilloscope. The pulse was connected to the oscilloscope with a BNC Tee adaptor, and the other side of the BNC Tee was connected to a length of coaxial cable.

Pulse Tester as TDR Test Setup

The initially launched and reflected pulses were captured as shown in the image below.

TDR Capture

Engineering Files
The Atmel Studio project, schematic, Gerber and BOM files are available for download using the links below.

Pulse Generator Microchip Studio Project

Pulse Generator Schematic Rev2

Pulse Generator Gerbers Rev2

Pulse Generator Bill of Materials Rev2

Amazon 9.8" Pottery Wheel Foot Speed Control Change

Introduction 
This short blog shows how to replace the speed control device in the foot controller on the Amazon 9.8” pottery wheel. This change may be required for anyone with irregular speed control or a damaged foot speed controller.

Determining the Part Replacement
With the pottery wheel unpowered, the internals of the foot speed controller are accessed by removing three plastic screws located in the base of the foot controller. The foot control mechanism consists of a potentiometer for setting the speed and two gears.

Internals of Foot Speed Controller

 To remove the potentiometer, the locking nut was loosened. This allowed removal and part identification.

Original Potentiometer

As shown in the above image, the potentiometer was rated at 4.7 k 2 W. A similar device was located from TE Connectivity part 3-1625931-0 and sourced online.

Replacement TE Connectivity Potentiometer

Items to Address with the Replacement Part
The TE Connectivity potentiometer is a direct replacement for its value (resistance); however, there are mechanical differences with the potentiometer, specifically the solder pins and smooth shaft. Since the original potentiometer was supplied with a D-shaped shaft, the original spur gear could not be reused, so a new spur gear needed to be created.

Original D-Shaft Spur Gear

Down the Spur Gear Road
The spur gear script feature in Fusion 360 was chosen to create a compatible gear. Alternative tools are available for creating a spur gear however these alternatives were not tested for this blog. Two alternative sites may be STL Gears and Gear Generator.

Fusion 360 Spur Gear Script
In Fusion 360, the Spur Gear script is accessed from the Utilities tab under the Add-Ins icon.

SpurGear Script in Fusion360

The settings in the image below were chosen after measuring the original gear, applying them to the spur gear script followed by 3D-printed prototypes. Some important items for the spur gear were the number of teeth, shaft diameter and Fusion 360 calculated Pitch Diameter.

SpurGear Settings in Fusion 360

Fusion 360 Spur Gear Modification
To ensure that the spur gear would not rotate on the round potentiometer shaft, two cutouts were added inside the spur gear shaft area for glue. The cutout changes were made to the spur gear sketch generated by the Fusion 360 script.

Editing the SpurGear Sketch

The images below show the edit to the sketch and updated 3D model.

SpurGear Sketch with Cutouts Added

SpurGear 3D with Cutouts Added

Ultimaker Cura was used to generate a print with a 100 % fill. The Fusion 360 file and STL files are available for downloaded at the end of this blog.

Replacing the Potentiometer
The wiring layout for the potentiometer was recorded. Using a soldering iron, the three wires from the original potentiometer were desoldered.

Potentiometer Wiring Connections

For the replacement potentiometer, the centre pin of the new potentiometer was determined to be the wiper (red wire). In the configuration shown in the image below, pressing the control pedal to the angled position increased the speed. For reverse operation, the yellow and green wire positions on the potentiometer should be swapped. All connections were soldered and covered with a piece of heatshrink.

Wiring for New Potentiometer

The replacement spur gear was printed in PLA and then it was placed onto the potentiometer shaft without glue to ensure it aligned with the other mechanism inside the pedal.

Positioning the Spur Gear

To ensure the gear did not rotate on the potentiometer shaft, glue was added.

Replacement Potentiometer with Round Shaft

Fitting and Setting the Potentiometer Home Position
With the connections finalised and the gear positioned, the locking nut on the potentiometer was hand-tightened.

Mounted Potentiometer with Threadlocker

The pottery wheel was powered and set up to operate from the foot control. In the horizontal position, the potentiometer was rotated so that the pottery wheel did not turn. This corresponds to a speed of 000 on the pottery wheel display. The potentiometer was tightened further. Pressing the foot control to the angled position resulted in a speed of 320.

Maximum Speed Value on Pottery Wheel

Loctite 222 was applied to the thread on the potentiometer to reduce the chance of the potentiometer coming loose.

Lastly, the base plate for the foot control was reattached and secured with the three plastic screws.

Downloads

SpurGear.f3d

SpurGear.stl