Oscilloscope - Ringing on Waveform Measurements

Introduction
This post is an aide-mémoire for enthusiasts performing measurements using an oscilloscope on circuits that feature fast rise-fall times.

Oscilloscope Measurement Ringing

Background
While reviewing waveforms posted online for Time Domain Reflectometry (TDR) circuits, some waveforms appeared to have ringing that may be a result of excessive lead lengths used during oscilloscope measurements.

Measurements
In this post, the example the rising edge of waveforms were captured using test equipment consisting of a 300 MHz 2 GS digital oscilloscope, a passive probe (calibrated) and a PSoC5 LP for signal edge pulse generation. The PSoC5 output pin was clocked at 4 MHz with a rise time of over 10 ns (Infineon-AN72382_Using_PSoC_3_and_PSoC_5LP_GPIO_Pins-ApplicationNotes-v09_00-EN.pdf, Greg Reynolds, Cypress, Rev H, 2018).

In the subsequent section, example 1 was the worst-case measurement for signal ringing and example 4 was an improved setup and measurement.

Example 1. Long Lead from Probe Tip and Long Earth Connection

Example 1 - Connections for Measurement

In this example, the cable lengths connected to the oscilloscope probe contribute mostly to the signal ringing. Other factors such as impedance mismatch were not reviewed as part of this post.

Example 1 - Oscilloscope Measurement

Example 2. Long Lead from Probe Tip and Leaded Oscilloscope Earth Connection

Example 2 - Connections for Measurement

Shorter cable lengths reduced the ringing however ringing was still prevalent.

Example 2 - Oscilloscope Measurement

Example 3. Direct Connection to Probe Tip and Leaded Oscilloscope Earth Connection

Example 3 - Connections for Measurement

This change to the connections was the largest improvement compared to examples 1 and 2. Ringing was improved with a direct probe connection and a shorter Earth lead although the return path through Earth lead could be reduced further.

Example 3 - Oscilloscope Measurement

Example 4. Direct Probe Tip and Ground Spring Connection

Example 4 - Connections for Measurement

 
A further improvement compared to example 3 with minimal lead lengths.

Example 4 - Oscilloscope Measurement

Example 5. Long Measurement Trace and Oscilloscope Earth Connection (Slow Edge Rate)

The capture below was made from the same hardware setup as example 1 and the PSoC was programmed for a slow instead of a fast edge rate.

Example 5 - Oscilloscope Measurement

Direct Connections
If a direct connection to a circuit board is possible, a board-mounted fixture in an option. These fixtures allow the oscilloscope probe tip to be inserted directly into the fixture. Some examples of fixtures for probing can be sourced from suppliers such as Teledyne, Cinch and Tektronix.

Example of Circuit Board Fixture (Courtesy DigiKey)

Summary
Attention to measurement techniques can improve oscilloscope measurements however these are not always practical. While this post touches on one possible change that can be made to measurements, other factors should also be researched and considered depending on the type of signal. Further literature and content including passive probe compensation is available from manufacturers such as Teledyne. Detailed content for oscilloscope measurements can be found from Analog.

Salvaging from a WAG120N Router

Introduction
This blog looks at salvaging parts and designs from a Linksys ADSL router model WAG120N.

WAG120N (Courtesy Google Images)

Parts Salvaging
Firstly flipping the router over to reveal the base of the unit, there are four plastic screws retaining the lid. After removing the screws, the lid can be detached from the base (two plastic shells) with a small flat-blade screwdriver or plastic prying tool.

Bottom View of WAG120N Router

Removing the lid shows the internals of the router; a circuit board and a dedicated antenna.

Internal View of WAG120N Router

Circuit Board - Top Side
The DC-DC Stepdown converter from ITE Tech part CAT7105CA (purple box in image below) is not listed as a part online; the status of the part is unknown. Not worth salvaging unless for a repair to a similar router.

Identified Parts of WAG120N Router Circuit Board - Top Side

The serial flash from Taiwanese manufacturer Macronix International, part MX25L3206EMZI-12G (red box), is not large in capacity but could be salvaged. As with other parts, this part appears to be obsolete.

Capacitor manufacturers are Leylon and Luxon. These parts appear to be in good condition although for the age of the router, these may not be worth salvaging.

There are two through-hole crystals on the board, 25 MHz and 36 MHz (black box). Depending on needs, either crystal could be useful for small or hobby projects.

Under the small aluminium heatsink is the part responsible for the 802.11 communications, Ralink RT3050F (yellow box).

Other parts such as the memory (green box), ADSL controller (blue box) and the enclosed metal can device were not reviewed. The remaining items such as the LEDs could be easily salvaged.

Salvaging the mechanical items such as the switch, power jack, push button and connectors could be possible with the appropriate equipment.

Circuit Board - Bottom Side
The linear regulator used on the board appear to be manufactured by General Semiconductor which was acquired by Vishay Semiconductor some years ago. The part on the circuit board GS117A (red box in image below) appears to be obsolete although this is a jelly bean regulator.

Identified Parts of WAG120N Router Circuit Board - Bottom Side

Some parts with markings, NF B1386L, are possibly a Unisonic transistor 2SB1386L (blue box), not worth salvaging.

External and Circuit Board WiFi Antennas
The external antenna pictured below from Galtronics could not be located as a product on the Galtronics website. The antenna may have been a custom design for the Linksys router.

Galtronics External Router Antenna

The mechanical antenna may be an interesting part to experiment with. For the second WiFi antenna, this is designed into the circuit board as pictured below.

Circuit Board Antenna for Router

Both antennas could serve as reference design in the WiFi domain by providing dimensions or a circuit board layout.

Summary
In general, the physical parts from the Linksys router were not worth salvaging. However, the dedicated external WiFi antenna from Galtronics was an interesting hardware design.

Voltage Interruption Tester for EN 61000-4-29 Code Update

Introduction
This blog provides a software update to the Voltage Interruption Tester discussed in previous posts

Code Changes
A simple software watchdog was added to the code. The watchdog duration was determined by measuring the maximum cycle time of the main loop with some additional time to account for jitter.

Decrementing counter was placed in the system timer.

/*******************************************************************************
* @brief System Timer
* @note  1 ms
*******************************************************************************/
CY_ISR(Timer_System_isr)
{         
    ...
    if (WD_Ctr != 0)
    {
        WD_Ctr--;
        if (WD_Ctr == 0)
        {   
            CySoftwareReset();      /* Should never get here */
        }
     }
    ...
}

Time timer was refreshed in main.

/*******************************************************************************
* @brief    Main
* @return   The point of no main
*******************************************************************************/
int main()
{
    ...
    while(1u)
    {
      ...
      WD_Ctr = WD_TIMEOUT;
    }
}

Downloads

Interruption Tester 0.1d PSoC Project

Hakko FM-2025 FM-2027 DIN Cable Connections

Introduction
This post provides the wire colours connected to the 8-way DIN connector for the Hakko FM-2025 and FM-2027 soldering handpieces. The information may help those repairing damaged or worn cabling on those handpieces.

FM-2025
This handpiece has no LED in the handle.

Hakko FM-2025 Soldering Handpiece

Hakko FM-2025 DIN Connections

FM-2027
This handpiece has a red LED in the handpiece.

Hakko FM-2027 Soldering Handpiece

Hakko FM-2027 DIN Connections

Note: The pin numbering taken from the DIN connector was not easily readable and should be verified.

Model Rocket Launcher WiFi ESP8266 Part 2

Introduction 
This blog continues from Part 1 of the WiFi-controlled rocket launcher. In this short post, load testing was performed on the igniter's power supply and the output drivers.

WiFi Rocket Launcher Blank PCB

Power Supply
The DC-DC converter, Texas Instruments part LMR50410, was tested for switch ON voltage threshold and response. Since the converter powers an ESP module and output drivers for the igniter, the load current test was set for 300 mA.

Power Supply Portion of Rocket Launcher

An external power supply was connected to the launcher board. The voltage was increased in increments of 100 mV until the converter activated. For this board, the threshold was 4.1 V. The output switch ON waveform is shown below.

Rocket Launcher Power Supply Supply Turn ON

A resistive load resulting in 330 mA was connected to the 3.3 V supply for testing. The output voltage dropped from 3.3 V to 3.28 V when the load was connected.

Rocket Launcher Power Supply Supply Transient Response

The transient response for the power supply was measured for a 50 % load change. Captured in the image above is the response showing a recovery time of less than 200 ns for the supply voltage to settle back to 50 mV.

Output Drivers
The output driver circuit design had been established from the previous version of the launcher circuit board, which meant the operation was already known.

Rocket Launcher Output Driver Load Testing

To test the output drivers on this board, a 5 Ω resistive load was used. The two output drivers were powered with 12 V to simulate the primary power source. Using the 3.3 V from the converter, the two drivers were activated.
V(supply) = 11.92 at drivers no load, V(supply) reduced 11.79 V with approximately 2.3 A load current because of cable losses.

Measurements were taken with 2.3 A of load current
V(load) = 11.19 V
V(diode) = 401 mV
V(high side driver) = 102 mV
V(low end driver) = 124 mV

In part 3, the code for the rocket launcher will be started in Arduino IDE.

Piezo Transducer Testing

Introduction 
This blog shows a piezo transducer's audible response to square waves. Measurements were performed using the software Friture with an external microphone.

Piezo Transducer

Background
Following an incorrect delivery of a piezo transducer instead of a piezo sounder, it was fascinating to determine how the device would respond different frequencies.

Test Device
A piezo sounder is a device containing the piezo element and related drive circuitry. The drive circuitry generates the necessary signal to drive the piezo element at a specific frequency.
The piezo transducer (piezo element) tested in this blog was a part (ABT-414-RC) that specified the external drive at a certain frequency.

The specifications for the transducer are replicated below from the datasheet.

ABT-414-RC Transducer Specifications

Testing
To measure the response of the transducer, a function generator was connected directly to the piezo. The function generator settings were made for a square wave at 0 - 3 V pk with a 50 % duty.

Image of Test Setup

Measuring the transducer sound output was performed using the software package Friture. Friture is an open-source easy-to-navigate real-time audio analyser.

About Friture

Friture was configured with the settings displayed below, A weighting for the measurements.

Friture Settings

The microphone for measurement was a Thronmax MDrill One Pro configured for cardioid mode.

Measurements (dB) were performed at 50 cm instead of the usual distance of 100 cm. These measurements were indicative.

Frequencies between 1 kHz and 4 kHz were set on the function generator, with measured values taken from Friture. Pictured below are the plotted results taken at 50 cm spacing between the piezo and microphone.

Plot of Measurements vs Frequency for ABT-414-RC

The operation of the function generator was then changed from a single frequency to a sweep. Frequencies were swept between 1 kHz and 6 kHz over a period of 100 ms.

In the screen capture below from Friture, the first frequency peak at 2.4 kHz is seen first. There was a second resonant measurement at approximately 5 kHz.

Plot from Friture for ABT-414-RC Frequency Sweep

The sweep response above shows that the drive frequency for the piezo transducer can vary by a more than 100 Hz with minor reduction in output level.

Lastly, the function generator output frequency was set to 2.4 kHz. The measurement from Friture is displayed blow.

Piezo Measurement at 2.4 kHz

 
Limiting Piezo Voltage
To limit voltages seen by the driving source, a device such as a general-purpose diode is recommended across the terminals of the piezo. The two oscilloscope captures below show the effect on the waveform with and without a diode across the transducer. 

When measuring the sound level with the microphone, the difference in measurements for a frequency of 2.4 kHz was less than 2 dB with and without a diode fitted.

Waveform at Piezo Transducer

Waveform at Piezo Transducer with Parallel Diode

 
Summary
A piezo transducer can readily replace a piezo sounder however, implementation will depend on the hardware utilised to drive the piezo. Circuit protection should also be reviewed as part of the standard impact analysis.

PCB Mouse Bites and Board Traces

Introduction 
This blog shows testing of circuit board mouse bites that have copper traces passing through them. The breaking strength of the mouse bite was also measured during testing.

Mouse Bite Test Boards

Mouse Bites
The use of mouse bites with circuit boards can be as varied as the application however, some common examples of applications include board panelisation, tooling strips, test coupons, in-circuit testing or breakaway boards. This blog’s focus is on small breakaway boards commonly used in embedded programming or development boards where traces are routed through the mouse bites.

SparkFun published a white paper in 2022 (Author, Nick Poole) that illustrated testing of various mouse bite combinations. The paper from SparkFun serves as a good reference for designer as it details the combinations and the force required to break the board under test (mouse bite).

This blog performs similar tests to those conducted by SparkFun however, the intent was also to see the effect of circuit board traces after breaking the mouse bites.

Test Board
A circuit board was created with four mouse bite configurations. The drill hole sizes varied between 0.38 mm to 1.00 mm. The pitch between holes was adjusted to suit the drill size and test boards.

Test Board for Mouse Bites

Between the holes of the mouse bites, traces were routed either externally (top and bottom) or internally traces (two mid-layers). This created eight combinations of trace and mouse bites for testing.

3D View of Test Board for Mouse Bites

Measurements
For each mouse bite break measurement, a simple setup containing an attachment to the test board and connecting wire to a digital scale was used.

Mounted Test Board

Measurement Tool

Results
The table below lists the test number against the mouse bite drill size and pitch combination. 

Mouse Bite Configurations

As seen in the chart below, there was little difference in test results between the various mouse bite configurations and lifted board traces. External board traces on average lifted on the opposite side of the circuit board. Any lifted traces were considered damaged. No internal traces were seen to be damaged.

Type vs Listed Traces After Testing

The chart beneath shows the average measurement (kg) required to break the mouse bite boards. A notable difference in the last two tests was expected because of the larger mouse bite holes meaning less circuit board material.

Type vs Measurements for Breaking Mouse Bites

The edge view of the main board in the image below shows the different breakage patterns.

Circuit Board Edge with Mouse Bites Removed

During two measurements, the test board broke cleanly except for one layer that lifted and tore away from the main board; as shown in the picture below.

Damaged Test Boards

Summary
The results in this blog with the specific test board indicate that internal traces experienced fewer issues with lifted traces. Other combinations of routing such as using a single side for external traces will likely be effective.

Mouse Bite Test Piece

For designs only requiring mouse bites in a circuit board design, most hole-pitch configurations are useable although the overall design should be reviewed as part of Engineering practices.

Risinglink PD201W Power Failure Detector

Introduction
This blog provides a teardown of the Risinglink PD201W Power Failure Detector and wall plug adaptor.

Risinglink Module

Power Failure Detector Supplier
The power failure detector is branded with the logo of the company Risinglink. There are no product specifications for the detector on the Risinglink website but documentation is provided with the detector when purchased.

Package Contents
A mains wall plug (USA), USB cable and documentation are shipped with the power failure detector shipment.
Opening the Detector
A thin flat bladed screwdriver was used to release the lid from the case. The joint near the R and K in the Risinglink logo was the optimum lid leverage position. The plastic lid has two clips to retain the lid in the housing.

Risinglink Module Internal

The ESP-12F WiFi module, CR2 battery, buzzer, switches and LEDs are immediately visible on the circuit board upon opening the unit. Removing the circuit board was possible by pressing the green LED away from the edge of the case. There are no components on the bottom side of the circuit board.

Risinglink Circuit Board

The battery manufacturer’s website (Tenergy) shows that the battery cell has a capacity of 800 mAh (Lithium). 

According to the ESP datasheet, operating the WiFi at continuous transmission draws an average of 71 mA. This would theoretically mean that a fully charged battery could monitor the status of the mains for hours.

As detailed in the documentation shipped with the detector, the white switch powers the detector with visual feedback provided by the red LED.

The black pushbutton is used to change operating modes as required when configuring the detector.

For the USB connector, only the power connections are utilised for monitoring the mains. No USB communication is possible to the detector. USB power is indicated through the illumination of the green LED.

Email Details
Notification emails are sent with “via amazonses.com” in the address. Emails events are received on the initial start-up, when a power outage occurs or when power restoration is detected.

The device PowerDetector started. Below is the device status at 01/01/2023 12:00PM.

• Power Status: ON
• Battery: 100%
• WiFi Signal: -51

As mentioned in the documentation, an email is sent after 24 hours if there is no communication with the module.

The device, ............, may be OFFLINE. No ping from the device within 24 hours. Please check WiFi connection, Internet service, etc. Please contact support@...... if any question.

Wall Plug
The wall plug (model HNT-H510) features an internal On-Bright controller responsible for the control aspect of generating DC 5V in either Constant Voltage (CV) or Constant Current (CC) mode. As the image from the wall below shows, the design is the usual compact solution.

Wall Plug Internals

ESP-12F
On the detector circuit board is an unpopulated 6-pin straight header (H1). Using the datasheet of the ESP-12F and a multimeter, the pinouts of the header were determined as displayed in the image below.

Pinouts for Risinglink Connector

A TTL to USB converter was connected to the header pins Tx, Rx and 0 V. An oscilloscope was used to measure the transmitted UART data bit time which was approximately 13.3 ms or 75 bps during bootup. Data was shown however this was not reviewed in further detail. Programming information for the ESP can be found on dozens of sites, on example here.

Example data on boot.
ets Jan  8 2013,rst cause:4, boot mode:(3,7)
wdt reset
load 0x40100000, len 30596, room 16
tail 4
chksum 0x3e
load 0x3ffe8000, len 2004, room 4
tail 0
chksum 0xa1
load 0x3ffe87e0, len 4752, room 8
tail 8
chksum 0x6a
csum 0x6a

Modifying the Power LED
Situated on the side of the detector housing is a green LED. When a 5 VDC USB power adaptor is connected, the green LED bursts into operation. The brightness of the LED may be beneficial for a large factory but for a confined space, the LED brightness may benefit from a reduction.

Bright LED on Risinglink Unit

The green LED uses a 1 k 0603 current limit resistor, R1. 

Resistor R1 on Risinglink Unit

To reduce the brightness of the LED, resistor R1 was increased to 10 k with the effects shown below. Resistor R1 was located between the green LED and the USB connector as shown in the capture above.

Dimmer LED on Risinglink Unit

 
Final Thoughts
The Risinglink PD201W is reasonably designed and simple to use. An option to use a custom email client over Amazon services would be preferable, especially for clients needing to security harden their network. 

Additionally, a helpful upgrade to the detector could be a battery-only access panel or a rechargeable battery.