Review: magnetic stirrer with heating plate and digital display XB 85-2

I purchased a laboratory style stirrer / hotplate with PID temperature controller for some experiments.

Above, the 85-2 product from Chinese maker XB.

It certainly looks the part and for under $100 looked impressive value… but was it?

Is it safe?

First thing with ANY Chinese appliance is to test the electrical safety. Prior to a full PAT test, I plugged it in on an insulated work space and waved a non-contact voltage detector over the case. Beeeep! The case is hot. Earth continuity (earth pint to case) is zero, there is no connection. This came with an AU plug… so lets look inside at how they wired it up.

The green yellow earth wire is floating look, the end has been tinned so it was or was intended to be soldered to something. The end of one of the screws holding four rubber feet on is more silver coloured than the others, so it appears to have been tacked on to that. Three issues: the screw tension is cushioned by the rubber foot and pressure to case is low so it would not be a reliable low resistance connection; soldered ground connections can melt off in a fault and are unacceptable practice; and the even this had become disconnected and would not have passed a basic electrical test. Chinese Quality!

So with the cover off, it is apparent just a few months after this May 2017 dated build has been put together with rusty steel. Continue reading Review: magnetic stirrer with heating plate and digital display XB 85-2

Last update: 21st September, 2017, 10:20 AM

Failure to treat impedance as a complex quantity leads to…

A ham recently posted a graph on QRZ to educate his fellow hams on the behaviour of transmission lines under mismatch.

Above is one of his graphs (the red arrow is my annotation). It plots Impedance variation along a mismatched 75Ω transmission line. The curves look graceful, but are they science or just pretty artwork? Continue reading Failure to treat impedance as a complex quantity leads to…

Last update: 22nd September, 2017, 6:08 AM

Demonstration of the GR1606B for antenna Z measurement and calcs

This article demonstrates use of a GR1606B RF impedance bridge for measurement of the feed point impedance of a MHz loaded mobile whip. The antenna is roof mounted on a vehicle and measurements are made looking into 4m of RG58C/U, then transformed to feed point impedance using three tools:

Key metrics are:

  • F=7.05MHz
  • R=35Ω
  • ReactanceDial offset=200
  • ReactanceDial=442
  • X=(442-299)/7.05=34.33Ω
  • Z=35+j34.33Ω;
  • Feed line is 4m of Belden 8262 (RG58C/U).

Continue reading Demonstration of the GR1606B for antenna Z measurement and calcs

Last update: 13th September, 2017, 10:57 AM

First full week of Amaysim broadband Internet access

iiNet

Review of 10 months of iiNet broadband Internet access detailed a fairly disappointing performance record of our first NBN based service, a 12/1Mb/s FTTN service from iiNet.

With a perception that online performance had degraded and was unsatisfactory, the results of an automated half hourly file download were consulted to verify those perceptions.

Above is a plot of the 90 percentile and 10 percentiles for each week. Continue reading First full week of Amaysim broadband Internet access

Last update: 11th September, 2017, 9:58 AM

4-20mA Pt100 input for the generic heating / cooling controller

The generic heating / cooling controller (hcctl) is a flexible bang-bang controller based on an ATTiny25.

The controller will accept 4-20mA input if the input is shunted by a 50Ω 1% resistor (2 x 50Ω 1% resistors is a practical implementation) and the 4-20mA sensor is wired between nominal +24 and the input pin. Note that 4-20mA sensors may operate properly on less than 24V (the one used here is a DIN rail mount that works for 10-24V).

 

To demonstrate the capability, a Pt100 RTD is connected to a 4-20mA converter and then to a hcctl test module (see above). The test module is driving a small incandescent lamp which is clipped to the RTD to provide a cycling test.

Continue reading 4-20mA Pt100 input for the generic heating / cooling controller

Last update: 14th September, 2017, 7:13 PM

ESP8266 remote power display for energy monitor – EV3 – 5V display

ESP8266 remote power display for energy monitor – EV3 documented an evolved design for a real power display using emontx3 / emonhub / mqtt. This article documents an adaptation to use a 5V display module (for higher brightness). The ESP8266 is not 5V tolerant, so a logic level converter is needed.

Hardware

The remote power display uses a Wemos D1Pro module, a common 5V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit, and a common 3V/5V logic level converter between them.

Above, the Wemos D1Pro prototype with wires attached to the HSPI and power pins. A 1k pull=down resistor is soldered between the D8 and GND pins under the D1Pro board. Continue reading ESP8266 remote power display for energy monitor – EV3 – 5V display

Last update: 16th December, 2019, 4:00 PM

ESP8266 remote power display for energy monitor – EV3

ESP8266 remote power display for energy monitor and ESP8266 remote power display for energy monitor – EV2 documented a design and some variations for a real power display using emontx3 / emonhub / mqtt. This article documents an evolution to use the ESP8266 HSPI port for much higher speed writing of the LED display, high enough to be later adapted for multiplexed displays.

Hardware

The remote power display uses a ESP8266-12E devkit 1.0 module, a common 3.3V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit. The particular LED module has sufficient space to mount the ESP8266 inside the module.

Above, the interior of the module that suits the implementation. Continue reading ESP8266 remote power display for energy monitor – EV3

Last update: 2nd November, 2019, 5:57 PM

Inside the YHDC SCT013 current transformer

The YHDC SCT013 series is very popular for use in energy monitor projects.

Disassembly

Warning, the core is VERY hard, but VERY brittle, don’t hit it with anything hard, don’t grip in with pliers, don’t drop it on a hard surface.

The coil and half core are held in the lower housing by two obvious catches which click over the bobbin. Removal means pulling the assembly upwards gently whilst releasing the catches and feeding cable into the housing. One of the catches will probably catch on the slot in the bobbin, be prepared to release it.

 

An ideal tool for the purpose is an ordinary $2 DIP chip puller which can be used to get purchase on the two ears on the bobbin that can be seen in this pic. Push a little cable into the housing, pull upwards while releasing the catches, then feed more cable and the assembly is pulled upwards from the housing.

Above is the PCB detail. This one has a TVS (the black component) and no burden resistors. There is a place for two parallel 0806 burden resistors on the board.

The PCB floats on two plastic pin extensions of the bobbin. You may obtain benefit in securing it with two very small fillets of hot melt adhesive as above, small enough so as to not interfere with the guide rails in the enclosure.

Burden resistors

So if you wanted to add a burden resistor for 0.333V out at 50mA secondary current, R=0.3333/0.05=6.6667. You could do this with 1% resistors in the E12 value series, 12Ω and 15Ω will give the desired resistance. Likewise for 1V out, 22Ω and 220Ω in parallel will give the desired value of 20Ω.

If you wish to remove existing burden resistors, they can be removed with specialised tooling but small SMD resistors will usually melt the other side solder moments after melting the first side. Position a toothpick with one had to push the resistor sideways, with the other and use the soldering iron to eat one side to melt, move the soldering iron to the other side and push the resistor sideways with the toothpick as soon as both sides melt.

Protection

A CT that has no load could develop extreme and damaging voltage within the secondary winding in the presence of primary current. If the CT assembly does not have an integral burden resistor, it is wise to install a TVS or pair of inverse series 9V Zener diodes to prevent excessive voltage lest the external load be disconnected.

 

Last update: 8th September, 2017, 10:58 AM

BG7TBL noise source

This is a review of the BG7TBL noise source available on eBay for about $20 incl post. I have seen this recommended in various online forums and thought it worthy of review.

A quick mention of Excess Noise Ratio (ENR), it is a commonly used measure of the characteristic of noise sources. A noise source for testing low noise RF amplifiers needs to be less than 10dB, 5dB is common; for other receiver testing around 15dB is common, and for massive output for filter alignment etc the noise needs to be well above a spectrum analyser noise floor so an ENR of 50dB might be appropriate (but such high noise output makes it useless for LNA noise figure measurement),

Above is the device. The layout is pretty simple, it is a Zener noise source at the left followed by three MMIC amplifier stages. The circuitry at mid left is a DC-DC converter to supply 25V to the Zener.

There are a host of aspects so far that are concerning:

  • there is no need to operate the Zener at such high voltage;
  • lack of regulation of MMIC power supply;
  • the noise output of the Zener source should be quite high; and
  • three stages of MMIC will give rise to huge output, notwithstanding the on-board attenuators at Zener output and final MMIC output.

Continue reading BG7TBL noise source

Last update: 7th September, 2017, 1:41 PM

ESP8266 remote power display for energy monitor – EV2

See ESP8266 remote power display for energy monitor – EV3 for an update…

ESP8266 remote power display for energy monitor documented a design and some variations for a real power display display using emontx3 / emonhub / mqtt. This article documents a simple compact implementation.

Hardware

The remote power display uses a ESP8266-12E devkit 1.0 module, a common 3.3V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit. The particular LED module has sufficient space to mount the ESP8266 inside the module.

Above, the interior of the module that suits the implementation. Continue reading ESP8266 remote power display for energy monitor – EV2

Last update: 18th October, 2018, 8:07 AM