Model Rocket Launcher WiFi ESP8266 Part 4

Introduction 
This blog is a brief update following on from Part 3 of the ‘Wi-Fi-controlled rocket launcher’. A design to replace the lead-acid battery in the launcher was assembled. 

Some field shots of the updated launcher are provided at the end of the post.

18650 Replacement for Lead Acid Battery
A printed circuit board (PCB) with two 18650 batteries was designed to replace the 12 V lead-acid battery used by the launcher.

The operating voltage of the launchers' ESP32 controller and the output drivers is around 3.3 V, meaning the parts were suitable for operation with the 18650 voltage. However, the main DC-DC converter (LMR50410YFQDBV) would need to be changed or bypassed, as its operating voltage is 4 – 36 V. The standard operating voltage of a single 18650 cell drops below the 4 V threshold of the DC-DC converter.

The Keystone Electronics 18650 battery holder, part #1043, was chosen for the PCB design. When selecting parts in the initial PCB layout, two 1043 battery holders were more cost-effective than a double 1850 holder, Keystone part #1049. The Keystone double battery holder had become the cheaper option at the time of writing.

Dual 18650 on PCB

The dimensions of the PCB were made to fit into the existing 3D printed launcher case.

Dual 18650 PCB in 3D

After the PCB was manufactured, a single Keystone battery holder was fitted. For connection compatibility with the spade tabs on the lead acid battery, spade connections were fitted on the PCB using TE Connectivity part #60465-2. As can be seen in the image below, the spade connections were secured to the PCB with M3 mounting hardware.

Partially Populated 18650 Board

Out of curiosity, the DC-DC converter on the launcher was run from a single 18650. First, the previous voltage divider created by the resistor pack RP1 was removed. The shutdown input on the DC-DC converter (LMR50410YFQDBV) was then connected to the supply (VIN) with a 10 R resistor.

Existing DC-DC Converter Shutdown Circuit

 

Modified DC-DC Converter Shutdown Connection

Using a fully charged 18650, the launcher powers ON briefly. When the 18650 voltage drops below 4 V, the DC-DC converter fails to turn ON and the output voltage becomes unstable. Having the PCB with different 18650 connection options may be part of the next board review.

Field Tested Unit
The two launches below are taken from a recent rocket day.

Salvaging Components from DPF-HD1000

Introduction 
This post looks at electronic components that could be salvaged from a Sony digital photo frame, DPF-HD1000 (circa 2010).

Tear Down
Four plastic screws secure the two halves of the photo frame case. A thin prying tool was used to release the internal plastic clips.

DPF-HD1000 Front Cover Removed

Removing the front panel shows the LCD and two peripheral items, an IR sensor and an LED strip.

Internals of the Photo Frame
Shifting the position of the display shows the main Printed Circuit Assembly (PCA) and the board to peripheral connections.

DPF-HD1000 with PCA Exposed

The IR receiver was connected with a 3-pin cable to the main PCA. The markings on the sensor appear to be 28m5 and E23, but there is no data available for the part online. The connections to the sensor could possibly be determined from the cable colours.

DPF-HD1000 LED Logo Board

The small LED PCA was labelled ‘logo LED board’ circa 2011. This board was used to illuminate the Sony logo built into the front plastic cover.

DPF-HD1000 LED Logo Board Powered

From the website Panel Look, the LCD appears to be from CPT, although discontinued, and could be used for repair or paired with a converter board capable of driving 60-pin flat flex cables from various interfaces such as USB.

DPF-HD1000 LCD Part Number

After removing the 4 screws retaining the PCA, the entire electronic assembly could be removed.

DPF-HD1000 Complete Electronics Assembly

Disconnecting all the peripherals from the PCA, attention turned to some interesting components on the main PCA. The PCA was labelled ‘Sony Basic 10DW MP’.

Possible PCA Component Salvaging
The USB connectors, surface mount and vertical switches could be salvaged from the PCA. The combination card holder on the PCA was an interesting component (large component on the right of the PCA); no data could be found from the A238B marking on the device.

DPF-HD1000 PCA Side 1

Upon reviewing the passives, inductors and the common mode filter near the DC jack (bottom right) these could be salvaged and reused. Due to the age of the PCA, the SMT electrolytic capacitors are not recommended for salvaging, although they did appear in near-new condition.

For active devices, the single linear regulator 1117T near the SD card holder could be salvaged.

DPF-HD1000 PCA Side 2

Flipping the PCA shows several chips, connectors for the peripheral devices and a smattering of passives. If any external devices, such as the IR sensor, were earmarked for salvage, the surface mount connectors could also be salvaged from the PCA.

To the left of the main Amlogic controller is a surface mount switch which may be responsible for detecting rotation (movement) of the display. When shaking the PCA, the internal mechanism can be heard moving. The component marking is EnSky, however no data could be located on the switch.

There is an oscillator, possibly 24 MHz (middle PCA), driving the Amlogic controller and a watch crystal for the on-board RTC (PCA bottom right) that may be useable.

An ELNA button supercapacitor, rated at 3.3 V 0.22 uF, provided backup for the RTC. Looking at the supercapacitor, corrosion was sighted on the case of the device and therefore not useable.

Corrosion on Supercapacitor

The main controller AML6236-VB-B is not listed on the Amlogic website and is likely not worth salvaging.

For storage, Sony opted for a Samsung 2 GB eMMC, part number KLM2G1HE3F-B001 (far left on PCA2). While this component does not appear to be manufactured any more, it would be a great device for experiments. The PCB model still appears to be available (SnapEDA). Even though the component may need to be reballed when fitting the component to a new PCA, connection to micros such as ST or Microchip would most likely be possible.

The 512 Mbit DDR1 memory was provided by Etrontech, part EM6AB160TSD-5G. This part could be used for repairs.

Interfacing the Amlogic controller to the LCD was a Texas Instruments flat panel driver part number SN75LVDS83B. The datasheet is an interesting read and even contains a good summary of PCB layout techniques.

Some other active components on the PCA are the serial flash, switching and linear regulators, speaker driver and RTC. There is also an unmarked chip on the board whose purpose is not clear. Many of these components could be salvaged depending on requirements.

Component Salvaging Example
Often questions posted after salvaging blogs relate to how components are removed from PCAs. As an example, consider the removal of the DC jack from the PCA.

Setup for Component Removal

The jack component is a 5-pin device that could be desoldered although in this example it was removed using a heater plate. Firstly, all the components on the opposite side of the DC jack were removed. These components consisted primarily of passives. This side of the board was made as flat and clean as possible. Then a heater plate, in this instance a MiniWare MHP50, was used to preheat the side of the PCA where the passives were removed (beneath the DC jack). Shortly after the heating cycle, a reflow cycle was run to pry the jack from the PCA. This technique certainly cannot be used for every board and component as the component population density and board construction can have significant effects on heating.

Salvaged DC Power Jack

Other tools such as a hot air desoldering tool or a small temperature controlled oven may be better suited for the removal of specific components.

Transponder Coil Test

Introduction 
This short post details the testing of the transponder portion of the tank circuit used for the ScioSense AS3935 lightning sensor.

AS3935 Block Diagram (Courtesy Sciosense B.V.)

Sensor Board for Arduino (Educational)
A printed circuit board (PCB) was designed for the ScioSense lightning sensor which was paired with an RGB LED (8x8) matrix as a visual output device for lightning intensity. The PCB design uses the common Arduino shield footprint to suit a controller such as the Uno or another compatible controller.

3D View of Lightning Sensor PCB

Tank Circuit Testing
After reading comments from several forums regarding sensitivity concerns with the AS3935, I wanted to check the Q-factor of the recommended LC resonant tank circuit for lighting detection. The transponder manufacturer, Coilcraft, has an article describing testing with a Helmholtz coil however I was interested in driving the recommended tank circuit with the function generator and then measuring the resonance with a second transponder coil connected to a scope.

Coil Coupled Tank Circuit Measurements
Using the two-board setup as pictured below meant that the distance and alignment of each board (transponder coils) affected the measurements. The placement of the transponders in proximity to each other impacts the field coupling. Field coupling is explained well at this Electronics Tutorials site.

Tank Circuit and Transponder Measurement Test Setup

During the test setup, the highest coupled transponder voltage on the receiver transponder was measured using an oscilloscope. The two boards were fixed in position for consistent measurements. Measurements using this test process are not perfect because of the coupling factor between the coils (not unity) and mutual inductance can also affect measurement accuracy.

Tank Circuit Measurements
The datasheet for the AS3935 recommends a 10 k resistor in parallel with a 1 nF capacitor and the transponder coil for the tank circuit.

Schematic of Tank Circuit on Test Board

A second board with only the transponder coil fitted served as the detector through a connection to an oscilloscope. 

The signal generator frequency was varied and measurements were taken using an oscilloscope. The approximate centre frequency (resonant) and the corresponding 3 dB points were determined during testing. 

From the centre frequency measurements and the 3 dB points, the Q factor was calculated. Three different resistor values were tested and the table below shows a plot of the resistor values and the calculated Q factors. For the recommended tank circuit, the resonant frequency was around 494 kHz.

Tank Circuit - Measurement Data

Tank Circuit - Plot of Resistor Value vs Q-Factor

As a validation test, the FFT function on an oscilloscope was used to view the changes in the resonant frequency of the tank circuit as the the signal generator frequency was varied.

Tank Circuit Measurement Validation using Field Probe

To perform the FFT measurements, a near-field probe (Beehive Electronics) was connected to a wideband amplifier and then connected through to an oscilloscope. 

Captured in the image below is the approximate resonant frequency of 488 kHz. The test board was fitted with the suggested design, a 10 k resistor, 1 nF capacitor in parallel with the transponder coil.

Tank Circuit - FFT Measurement

Final Thoughts
A standalone transponder coil was used in this post to show that a parallel RLC circuit on a different circuit board was resonating. Validation of the resonant frequency using a field probe indicated that the measurement difference between using a second transponder coil for measurement, or a field probe was less than 2 %. For accurate resonant frequency measurements, factors such as mutual inductance in the measurement device and the equipment under test should be accounted for.

Crosstalk Test PCB (Educational)

Introduction 
The Printed Circuit Board (PCB) design in this post was inspired by the well-known signal integrity educator, and professor, Eric Bogatin. The board design was based on content shown in a YouTube video created to demonstrate crosstalk.

Crosstalk PCB 3D

Why This Design?
Following on from the PCB trace-to-trace crosstalk content created by YouTuber Robert Feranec with guest Eric Bogatin, I wanted to design a simple educational board that would allow crosstalk measurements to be made on a PCB and tested when passive elements were introduced into PCB traces. Crosstalk measurements with series and parallel resistor signal path terminations are common in many PCB designs and this PCB design was designed specifically for series terminations.

Circuit Board Design
A regular 1.6 mm board (FR4) double-sided PCB was chosen for the design. For the copper layers, a reference plane was placed on one side of the PCB and impedance-controlled traces were placed on the opposite side. Using PCB design software tools, the configuration of the trace impedance (width) was tuned for around 50 R impedance giving a 2.8 mm trace width. The 50 R impedance is given a tolerance of + 10 % as this is the standard tolerance for PCB fabrication houses in the local region.

Altium Impedance Profile 50 R for Crosstalk PCB

 

As a crosstalk PCB design features two signal traces, the spacing between the traces was set at less than a track width to ensure ample signal coupling between traces.

Crosstalk PCB 2D

As the series element, a resistor footprint was included in one of the PCB test traces.

Crosstalk PCB Resistor Linked

This footprint on the PCB provided an option to test with different resistor values and then measure the effects with suitable test equipment. A pulse generator with a fast edge and an oscilloscope are required.

The first setup on the test PCB has the series resistor on the same layer as the signal trace and the second test setup has the resistor on the opposite side to the trace, connected through vias.

Board Build and Initial Testing
For the board assembly, the Molex SMA connectors were fitted. The Molex part number is 0732512120. For the validation test, the resistors on the PCB were replaced with solder shorts.

During testing, the trace with the series resistor is referred to as the aggressor and the nearby sensing trace, is the victim. Further details relating to this setup and a further explanation can be found in the aforementioned video content with Robert Feranec.

First Test Setup with Crosstalk PCB and Pulse Generator

For validation, measurements were taken using an oscilloscope with a bandwidth of less than 500 MHz and a simple pulse generator (Microchip version) designed in a previous blog.

Pulse Generator Frequency

Pulse Generator Rise Time

With the pulse generator providing the 1.4 ns rising edge signal into the aggressor trace (CH2 blue trace), the connector at the near end of the victim trace (CH1 yellow trace) was connected to the oscilloscope.

Near End Crosstalk PCB Measurements

For a second measurement, the two ends of the victim trace were connected to oscilloscope. When the pulse was applied to the aggressor,  the signal entering and then reflecting (near and far end) was measurable.

Near and Far End Crosstalk PCB Measurements

Summary
This short post introduced a printed circuit board for testing the behaviour of signals relating to crosstalk measurements. The option to use a series resistive element was included but not tested in this post. 

The PCB Gerber files are downloadable using the link below for those who prefer to build the board and perform testing at home, school or in the lab. The Gerber files use the format as defined on this page.

Crosstalk PCB Gerber Files