Month: May 2021

SNTP synchronised clock v1 – boxing it up

The SNTP synchronised clock (ssc) is an ESP8266 based time of day clock with an LED display.

The code is fairly mature, and the boxed prototype will be build with a large 4 digit 7 segment LED display (1.2″ or 30mm) using the HT16K33 driver chip.

The prototype will be housed in an ABS Jiffy box, and a new lid cut from dark red transparent acrylic on the CNC router.

Above is the sketch of the layout. The screw holes in the display are M1.6, and there is no clearance for larger screws. Continue reading SNTP synchronised clock v1 – boxing it up

Last update: 13th June, 2022, 2:26 PM

EB104 alternative output circuit

One of the very important designs of HF broadband MOSFET power amplifiers was that of Helge Granberg in Motorola application note EB104.

This article offers an explanation of how the the alternative output circuit at Fig 5 of EB104 works.

Let’s look at the schematic diagram of the PA.

Above is the schematic from EB104, of interest for this article is the output circuit comprising T2 and T3 which are intended ideally to provide a drain to drain load of 50/9=5.55Ω. Continue reading EB104 alternative output circuit

Last update: 25th May, 2021, 10:05 AM

A desk review of the MiniPa100 kit – #2: transformer T2 turns ratio

This article is on in a series of a desk review, a pre-purchase study if you like, of the MiniPa100 kit widely sold on eBay and elsewhere online.

Previously…

The above pic from an eBay advertisement of the 2020 version of the PA would suggest very strongly that there are three turns on the secondary of the output transformer, and a half turn on each drain. Interestingly the 70W versions also appear to use three turns, alarm bells ring!

Here is a little table that shows the maximum power obtainable with a transformer of this type for various supply voltages and secondary turns. Continue reading A desk review of the MiniPa100 kit – #2: transformer T2 turns ratio

Last update: 11th June, 2021, 7:42 AM

Desk study of M0DGQ’s 150W HF PA

M0DGQ described a broadband HF PA in the Wythal Radio Club’s newsletter 2017-01, and rated it at 150W output. Note that this module does not include the necessary output filter which will probably lose 5-10% of the power from this module.

The PA uses a MRF9180 dual MOSFET operating on 26V supply.

Above is the prototype PA. The text states very clearly that the output transformer uses a secondary of two turns of PTFE insulated wire, and the pic above does not provide evidence to the contrary.

Hmmm, experience suggests that may be too few turns. Continue reading Desk study of M0DGQ’s 150W HF PA

Last update: 10th July, 2023, 8:26 AM

A desk review of the MiniPa100 kit – #1: characterise the output transformer

This article is one in a series of a desk review, a pre-purchase study if you like, of the MiniPa100 kit widely sold on eBay and elsewhere online.

One of the first questions to mind is whether it is likely to deliver the rated power, so let’s review the MOSFET output circuit design from that perspective.

Sellers mostly seem to need to obscure the MOSFET type in their pics, so essentially you buy this with no assurance as to what is supplied, no comeback if the supplied MOSFET is not up to the task. Online experts suggest the MOSFET is probably a MRF9120 (or 2x IRF640 in a 70W build). The amplifier claims 100W from 12-16V DC supply.

Note that this module does not include the necessary output filter which will lose 5-10% of the power from this module.

In this case Carlos, VK1EA, connected a sample output transformer (T2) core from a recently purchased MiniPa100 kit to a EU1KY antenna analyser. The fixture is critically important, it is at my specification. Continue reading A desk review of the MiniPa100 kit – #1: characterise the output transformer

Last update: 11th June, 2021, 7:41 AM

SNTP synchronised clock v1 – display options

The SNTP synchronised clock (ssc) is an ESP8266 based time of day clock with an LED display.

Code development progresses and a working prototype exists with three display options.

Directly supported 4 digit 7 segment LED displays

Several common driver boards are supported directly by the source code, most of these and variants can be purchased online for small money.

HT16K33

Above is a large 4 digit 7 segment LED display (1.2″ or 30mm) using the HT16K33 driver chip. Continue reading SNTP synchronised clock v1 – display options

Last update: 13th June, 2022, 2:25 PM

SNTP synchronised clock v0.01 – a preview

The SNTP synchronised clock (ssc) is an ESP8266 based time of day clock with an LED display.

Design criteria

The design criteria are:

  • small, portable, powered from a 5V USB power supply;
  • synchronised to a SNPT (simple network time protocol) server;
  • flexibility for a range of displays (74HC595 static, TM1637, HT16K33);
  • configurable time zone offset and daylight saving offset;
  • configurable from a web page;
  • switchable HH:MM and MM:SS display formats; and
  • switchable daylight saving mode.

The concept is that it is synchronised to net time, and the only adjustment needed through the year is to flick the daylight saving mode.

The hardware comprises:

  • ESP8266 dev board of some kind;
  • 5V to 3.3V power supply; and
  • 4 digit 7 segment LED display, preferably with a colon in the middle.

Above is a development prototype using a Wemos D1 mini ESP8266 board and 4 digit display using 74HC595 shift registers. Continue reading SNTP synchronised clock v0.01 – a preview

Last update: 17th July, 2022, 7:42 AM

Fix for a certain TM1637 LED display

There are a miriad of low cost displays for hobbyists in online shops, particularly targeting Arduinos where libraries exist to drive the most common chips.

This article looks at a 4 digit LED module particularly suited to a digital clock display. The driver chip is a TM1637, and it requires Vcc and Gnd, a data IO wire and data clock wire.

Above is an example that just didn’t work. Continue reading Fix for a certain TM1637 LED display

Last update: 14th May, 2021, 6:37 PM

Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’ #2

On review of the Ultrafire XML-T6 torch, I found the mode switching / mode memory so dysfunctional that it rendered the torch useless in my evaluation.

At Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’ I gave a fix for that revision of the electronics, and updated it with description of a later fixed production model.

Years later, I bought two more of these due to switch failures on the originals… and guess what, the flash on power on returns.

Let’s pull them apart.

They have a new revision / version of the LED driver PCB, and it has provision for a resistor in parallel with the capacitor, but the resistor pads are not populated.

Above, the LED driver board with a 100k resistor added, it is the far component. This was an 0805 part that was on hand, but ideally should be a 0603. Continue reading Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’ #2

Last update: 12th May, 2021, 2:20 PM

ESP8266, ESP32 reset – the (ugly) detail

Like many microcontrollers, the ESP8266 and ESP32 series contain an in-Silicon bootloader which can be initiated at chip reset by holding a pin low at the moment of reset.

Documentation is not helped by less than common terms (like EXTRSTB for a pin that is really a /RST, and the EN pin which seems to be used interchangeably as a /reset pin). The other relevant pin is known as GPIO00, but can be thought of as a /BOOT bin (often labelled IO00 on PCBs).

Automatic bootloader initiation

The firmware is uploaded using ordinary RS232/TTL, and it is possible to use modem control signals to control the /RST (EXTRSTB) and /BOOT (GPIO00 or IO0) pins, indeed the common convention is to use RS232 signals RTS for resetting the MCU, and DTR for boot selection.

So, it is possible to connect RS232/TTL /RTS to /RST and /DTR to /BOOT, and ESPTOOL will automatically initiate the boot loader when accessing the chip.

Above is a simulation of that type of direct connection. The RTS/DTR scenario is that from ESPTOOL, but it can be seen that even if the RTS transition was delayed somewhat the /BOOT pin is low and when /RST rises the chip will initiate the bootloader. The critical timing is that /BOOT is low when /RST transitions from low to high. Continue reading ESP8266, ESP32 reset – the (ugly) detail

Last update: 28th March, 2022, 8:29 AM