Category: Electronics

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

ESP8266 remote power display for energy monitor

This article documents remote power display for an energy monitor system based on emontx3 / emonhub / mqtt.

The remote power display connects via WiFi and subscribes to a topic on a MQTT server, updates are published every 10s with data from the emontx3 by emonhub.

Hardware

The remote power display uses a Wemos D1Pro ESP8266 module, a common 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit, and a simple 3V/5V level converter between the two (see above shrink wrapped in the cable from the D1Pro to the display).  Continue reading ESP8266 remote power display for energy monitor

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

Inductance of a loop of CAT5 pair

An online expert recently reported:

I tried to make an antenna loop for longwave with cat 5 and after it did no good I realized the twisted wires canceled each other out.

Or did they really cancel?

Parallel connection

I constructed a loop of one Cat 5 pair and measured its inductance when both wires are bonded at the ends.

The conductors are 0.5mm diameter and spaced 0.9mm. To estimate the inductance we use the geometric mean radius (GMR) as the equivalent radius of the pair. GMR=(0.5*0.9)^0.5=0.67, diameter=1.34mm. So let’s calculate the inductance of a single turn circular loop of 0.8m perimeter and round conductor of 1.34mm diameter.

The estimate above is 850nH.

Above is the measurement, the screen is not readable, but it is 852nH, very close to the estimated 850nH. Continue reading Inductance of a loop of CAT5 pair

Last update: 2nd September, 2017, 8:52 PM

Inductance of sensorless brushless DC motors

A reader of A Demagnetisation Risk Index for a sensorless brushless DC drive asked whether the inductance of a sensorless brushless DC motor could be measured with one of the inexpensive LC meters available on eBay.

Motor inductance line-line typically ranges from several µH up towards 100µH. Importantly, the fundamental frequency of flux change in the laminated iron core under normal operation is typically less than 2kHz.

Validation of the LC200A

To verify the instrument, a test inductor was made with 3t on a FT-240-43 ferrite core.

Above is an estimate of the expected inductance of the test inductor, 9.65µH. Keep in mind that the tolerance of ferrite is quite wide, 20% variation is not unusual. The test inductor measured 9.1µH at 10kHz on a classic RLC meter.

Above, the LC200A measuring an inductor comprising 3t on a FT240-43 ferrite core, measurement frequency was 670kHz. The measured inductance is 8.98µH, 7% lower than the estimate but well within tolerance of the ferrite core, and less than 2% below the value measure with a classic RLC meter. Continue reading Inductance of sensorless brushless DC motors

Last update: 22nd August, 2017, 9:56 AM

SCT-010-000 current transformer protection

The YHDC SCT-010-000 clip-on or non-invasive current transformer is widely used in DIY energy monitor applications, and is readily available on eBay for A$6 including post.

A key issue with current transformers is that current in the primary winding will cause excessive voltages in the secondary winding unless the secondary winding is suitably loaded. The broad rule of thumb is NEVER disconnect the output connections whilst current flows through the primary.

 

YHDC’s website is typical of Chinese web sites, and I could not find a datasheet for information on the internal circuit and possibly internal protection.
Continue reading SCT-010-000 current transformer protection

Last update: 14th August, 2017, 3:52 PM

Review of Hantek DSO8102E hand held oscilloscope

This article is a brief review of some issues that were found with initial testing of a Hantek DSO8102E two channel 100MHz hand held oscilloscope.

The DSO8102E is a member of the DSO8000 series (DSO8060, DSO8070E, DSO8100E, DSO8150E, DSO8200E), and shares most specifications across the series.

The specifications are very impressive, and price at just under $1000 for a Chinese brand seemed reasonable (hand held oscilloscopes are expensive compared to bench oscilloscopes).

The test scenario was a practical application, observation of the data traffic to/from a DHT22 temperature and humidity sensor in the project ESP8266 IoT DHT22 temperature and humidity – evolution 2. Continue reading Review of Hantek DSO8102E hand held oscilloscope

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

ESP8266 IoT DHT22 temperature and humidity – evolution 3

This article documents a first project with the Espressif ESP8266 in its third evolution (based on ESP8266 IoT DHT22 temperature and humidity – evolution 2).

The objective is a module that will take periodic temperature and humidity measurements, and in this evolution publish them using a RESTful API.

Evolution 3

The example platform used in this article is a Wemos D1Pro. In this case, the D1Pro is configured for an external antenna, and a modification is made to the board to add a 1N34A diode for the deep sleep reset circuit (NodeMCU devkit V1 deep sleep). A three pin right angle header to the top of the board (as seen) and another on the underside on the opposite edge to get GND, +5, +3, and D4 for the DHT22 data wire. There is less than $20 in parts in the pic above. Continue reading ESP8266 IoT DHT22 temperature and humidity – evolution 3

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