Author: Woody

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TPL5110 as a Monostable

Low Quiescent Standby Current Power Switch

After finishing a recent project I had a heap of resistors that had been used as select on test parts and now needed sorting and storing correctly. I found a design on the web for a simple Arduino based autoranging resistance meter. I prototyped the measurement circuitry for this and it worked fine. I wanted the power to the device to be from a battery source and to have this turned on via a push button switch and to auto time the ON period and return to standby.

My immediate thought was to use the ICM7555 CMOS equivalent of the ubiquitus 555 as a monostable but although manufactured in CMOS technology it does have a relatively high standby current. Some web research led me to the Texas Instruments TPL5110 which can be used as a monstable triggered from a push button. The device has an incredibly low standby current of a few uA. To use the TPL5110 as a monostable is quite simple. The EN pin is tied to ground instead of to supply. The resulting section of circuitry is simple and is shown below.

The push button sits across the U$7 (supply rail) and U$8 (trigger) terminals and the ON period of the monostable operation is adjusted by the R22 trimpot. A 10 second ON period needs around 10K. Ignore the use of parallel resistors (R21 and R18) as this was to allow my PCB layout to use either a through hole part or SMD part. The switching FET for the supply is a commonly available P channel part. The particular part chosen (DMG3416) has a very low ON resistance. Note that the TPL5110 cannot be used over 5V.

The result is very legant and simple. The standby current was so low I struggled to measure it.

Note that Adafruit has a ready made module that uses the TPL5110 but this is configured with EN permantly connected to the incoming supply. In this mode the device is intended as a timing reference to turn projects ON and OFF at regular intervals in association with feedback from an associated microcontroller (via the DONE pin). If you look at the Adafruit PCB layout you will see that you will need some delicate hacking to get at the EN pin as this is linked to the incoming supply under the TPL5110.

More will follow on the completed Resistance Meter project which has an OLED display and 3D printed enclosure.

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Kindling Cracker – a safer option

Better late than never

Four weeks ago I had an argument with my wood chopping axe. . While chopping wood against a wobbly tree stump, the stump wobbled and the axe came down on my thumb end. I didn’t feel it but it took off the tip of the bone and the severed end was only hanging on by a very thin section. My wife got me to the local A&E and a very nice paramedic cleaned and strapped things together. Since then life has been fairly miserable as I battle with buttons and being unable to do much in the workshop.

The wound is now less tender and the size of the bandage is getting less bulky. I have been warned it could take months to get any sense of feel in the tip. The problem I most stuggle with is trying to ‘unsee’ the flash back image of my thumb with its end hanging off.

In the course of recounting the incident to her golfing friends my wife was told of the Kindling Cracker. This is a wood chopping gizzmo invented in New Zealand by a young lady as a school science project . There are various YouTube videos of this device on their website. It reverses the chopping process and has the axe blade stationary with the wood being impalled in it and bashed with a club hammer. A protective ring keeps flesh away from the sharp bits.

As I have been out of action in the wood chopping department, we bought a Kindling Chopper and my wife has taken over wood chopping responsibilities. She can now split wood like a check shirted lumberjack. It is a simple but elegant design. I agree it is not as quick as chopping by hand but it needs much less effort and the chore can be delegated safely to other members of the family.

The only problem is I discovered it four weeks too late and I have got a few months left to dwell on my stupidity.

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I had a ChatGPT experience

In deep shock and still coming to terms with it.

I am currently working on a timing synchroniser for the local church clock. Being of that generation I had come up with a CMOS based phase detector with monostable timers etc. This logic looks at the relative timing of the clock strike activation and a DCF timecode reference clock. I prototyped the circuitry, proved it and made a PCB for it in Fusion. It works very well and the resulting output slows or speeds up the clock by adding or removing lead shot to the weight tray on the clock pendulum.

I got my ear bent for being so old school and not using an Arduino or similar but I was reluctant to stray from known and proven simple logic with RC time constants. In the end I caved in and out of curiosity thought it might be a good project to get my feet wet with ChatGPT.

It took a little while to find my way round the ChatGPT site and to get to the software support section. Once there I entered in simple language what I was trying to achieve. ‘It’ replied with its understanding of my needs and I agreed this was correct. I then asked for some code for an Arduino UNO.

Out popped 44 lines of Arduino code …. which worked. Oh my goodness, what a revelation. Think I need to have a cup of tea and biscuit to recover. Like Fusion and 3D printing, this is going to completely change my workflow and project practices.

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Fusion Sheet Metal model export as PDF

Not quite so obvious export route

The Sheet Metal module in Fusion allows you to create a 3D model of a folded sheet metal part and then ‘flatten’ the model to provide a net shape with fold lines. It is quite easy to use and impressive in the results you can achieve. The model can be adjusted for different metal types and their properties. The resulting flat net can then be exported as a DXF to send off to a laser or water cutting sub contractor.

The Fusion Sheet Metal module only allows the flat net data to be exported as a DXF file. This is not surprising as this is the most common data file request from sub contractors. That having been said I recently had a request for a PDF file which at first glance is not an export option in the Sheet Metal module. One solution was to use a web based DXF to PDF converter but this could be potentially unreliable in the conversion result.

A less obvious solution is once you have created the unfolded (flat) net, open the Drawing module in Fusion and use the From Design option.

This will load the unfolded net into a Fusion Drawing with the ability to be exported in PDF format. This is quite a useful export route to take as you can dimension and annotate the drawing in more detail than would be possible in the standard DXF format export from the Sheet Metal module.

The use of this Drawing module export route is going to be fairly rare but it is a useful option to know about and have up your sleeve.

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SINO SDS2MS DRO repair

It turned out to be an easy fix

The SINO SDS2MS is a relatively old DRO control and display box. The owner of the unit brought it to me for a ‘look at’ after it had suddenly died after many years of faithful service. The internals consisted of a power supply and a PCB motherboard. The feed from the power supply was a two wire connection and the PCB clearly stated this was 5V. I isolated the connection and measured the power supply in isolation which revealed the power supply was only delivering 3V. Feeding the motherboard direct from a bench power supply at 5V brought the unit back to life. Current drawn was around 1 Amp.

I had in stock a MakerHut 5V/2A power supply that would physically swap out for the original power supply. I have used a lot of the MakerHut PSUs and found them to be very reliable. So problem solved, unit back up and running.

Reading around about the SINO units, it seems the power supply is the most common mode of failure. Comparing the size of the old PSU and the replacement unit gives an indication of how technology has changed.

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