I bought a little 4-20mA source on eBay for under $10.
The device has a backlit LCD display, and a rotary encoder with steps of 0.05mA (or 0.3125% of 16mA). The current setting can be set as power on default by pressing the knob. It is supplied with a 250Ω resistor which could be used as a load resistor in projects delivering 500mV FSD.
Continue reading Inexpensive 4-20mA source – review
The 4-20mA loop used for the water sensor needs a source of 24VDC. This is obtained from the battery (3.6-4.3V) using a DC-DC boost converter which runs only when a measurement is made.
This article discusses related issues. Continue reading IoT water tank telemetry project – part 4
It seems that almost all small DC-DC converter modules listed on eBay with LM2577 in the headline actually use the Chinese XL6009 chip which they may or may not state “replaces LM2577”.
But… is it a replacement? Continue reading XL6009 DC-DC converter chip issue
The project continues, albeit slowly.
Some inexpensive DC-DC boost converters have been very slow from China, though multiply source, they have not yet arrived.
An older module which was on hand has enabled progress of reliability and battery trials.
Above is the current prototype. The module on the white plug in cable is a 4-20mA simulator set to 20mA for maximum drain during battery trials. The module at upper right of the pic is a TP4056 batter charger and 1S protection board for the 2000mAh LiPo. The PV array (partially obscured) is capable of 80mA of charge current in full sunlight. The prototype includes a red LED drawing 1mA, an additional 24mAh load per day. Continue reading IoT water tank telemetry project – part 3
I have a ceiling fan which has poor balance and is quite annoying on its high speed.
To solve the problem, I attached a flight controller board which I had on hand for this sort of purpose to the stationary spindle extension, and I have the associated configuration software installed for flying machines
Above, the OmnibusF4 v1 flight controller. Not a good flight controller for flying machines because of the silly pinout, but cheap (for that reason), about $20 on eBay. The flight controller contains a 3 axis gyro and accelerometer, the latter will be used here. Continue reading Balancing a ceiling fan
This article is documentation of a capacity test of 5 x Hobbyking 2500mAh 18650 LiIon cells (9210000181-0).
The cells were purchased on 26/02/2018 (~$7 + shipping) and received at about 30% charge. They were each charged in a XTAR VC2 Plus charger at 0.5A until charged.
The cells are 65mm long, and do not claim to contain protection modules which are prudent in some applications.
Each cell was then discharged at 1A (0.4C) to 2.8V, the discharge was captured.
Continue reading Hobbyking 2500mAh 18650 LiIon cells (9210000181-0) initial capacity test
Calibration of the 4-20mA input
This article is a tutorial on calibrating the 4-20mA input which is designed for flexibility that is achieved through exploitation of the calibration.
The input device for this tutorial is a Pt100 RTD temperature sensor and inexpensive Chinese Pt100 – 4-20mA converter (loosely) calibrated for -50-150°. The Pt100, the converter, the load resistor, the divider resistors on the MCU board, and the MCu voltage reference all introduce error which is compensated in this end to end calibration procedure.
For this demonstration, two scenarios are measured:
- probe in still air whose temperature is captured with an accurate thermometer; and
- probe in boiling water whose temperature is calculated from known altitude and barometric pressure.
Another option would be to use a container of water filled with ice to obtain close to 0° for scenario 1… you don’t need a triple point cell for the end system stability and accuracy.
Temperature of boiling water
Using Calculate cooking time for soft boiled egg :
No, we are not boiling an egg, but the results include the temperature of the boiling water under current altitude and pressure. Continue reading IoT water tank telemetry project – part 2
This is the first in a series of articles describing a simple maker / DIY IoT water tank telemetry system.
- capture water depth, temperature and relative humidity;
- IoT connectivity;
- solar / battery powered;
- wireless connection;
- use existing inexpensive electronic modules.
Design choices made initially:
- 4-20mA water pressure sensor for depth measurement;
- ESP8266 Wemos D1 mini pro for the MCU and wireless elements;
- NodeMCU / Lua software environment;
- external antenna for improved WiFi range;
- 6V 100mA PV array;
- module with TP4056 batter charger and cell protection chip;
- 2500mAh 18650 cell;
- AM2320 temperature and humidity sensor;
- bipolar transistor switch for boost converter;
- Thingspeak RESTful interface for data accumulation and presentation.
Above is a block diagram showing the major system components. Almost all of the electronics is on easily obtained low cost electronic modules source from eBay, assembled on a Veroboard backplane. Continue reading IoT water tank telemetry project – part 1
A recent purchase of an inexpensive ($6) speaker polarity tester prompted a need for a stand alone driver for speakers.
Above, the tester has a microphone that senses the polarity of the pressure wave and indicates with one of two LEDs.
The tester comes with a CD containing a file that can be used to provide the test signal on a complete system with CD player, but there is a need for a stand alone driver for testing bare speakers or speaker units. Continue reading Speaker tick generator (for polarity testing)
Two bare dimmer modules sold on eBay with identical specification and similar price are compared.
Both claim to have zero hysteresis.
Zero hints a lie!
Hysteresis is caused in simple phase control dimmer circuits at low settings because in each half cycle the trigger capacitor starts at a different voltage depending on whether the diac fired on the previous half cycle.
A serious issue with this snap-on effect is that if power is turned off at low power setting and re-applied, the controller may not switch on.
Above is type 1, a very triac basic phase control circuit. The red capacitor and resistor to its left are snubber components, the yellow capacitor, 4.7kΩ resistor to its left and the 500k pot are the phase delay circuit, the diac is just visible above the red capacitor. Continue reading A comparo of two bare light dimmer modules