Difficulty Operating Solenoids with an Arduino Uno

[John HaineParticipant @johnhaine32865]

Having earned my crust in electronics for 45 years, and it's still paying my pension, I can't imagine going back to an analogue meter. AVOs were in their day the standard instrument but are now outmoded. Given a good-enough DMM is about £20 and you can buy a simple kit to make an oscilloscope that's good enough for simple debugging for the same if you're prepared to build it, I can't see any benefit in using an AVO unless you already have one. I used to have an AVO Minor, having not used it for 20 years or more I tested it a few weeks ago and the movement stuck at several places on the scale so it has been recycled. I also have 3 DMMs which all get used, as well as an old analogue 'scope and a new digital one – again only the modern scope is used for 99% of the time, in fact since I bought it I can't remember using the old Scopex one.

[SillyOldDufferModerator @sillyoldduffer]

Though I'm in John Haine's not impressed camp, I do own an AVO8, which was a gift. Like most tools it has virtues and shortcomings! For me the shortcomings outweigh the meter's advantages but we're all different.

In favour:

• Precision instrument (outstanding back in the day)
• Built to last and to take abuse; a practical rather than a laboratory instrument. Exceptionally solid construction – thick Bakelite front-panel mounted on a steel box. Further protected by a heavy leather case.
• Large easy to read scale with consistent calibrations.
• Well thought out ranges
• Does both DC and AC amps up to 10A
• Analogue movement gives quick indication of life in a circuit when actual values don't matter

Disadvantages:

• Very expensive new. Hobbyists own them via Government Surplus, ex-professional, or ex-educational. Often expensive second-hand too because people crave quality rather than functionality. Seriously expensive compared with modern alternatives (where modern means anything later than 1970!)
• Take up lots of bench space
• Heavy to carry (shoulder-strap job)
• Analogue movement slows down taking accurate readings. To be accurate the user has to select the most suitable range, and to read the scale carefully, including reducing parallax with the mirror. Also has to get the polarity right!
• By modern standards Avo 8 accuracy is ordinary, many cheaper meters do just as well.
• The Avo's relatively low impedance makes it dodgy for electronics – it was designed for valves, not low voltage semi-conductors.

For what it's worth, I use an ordinary 20kΩ analogue meter and a hand-held Digital Multimeter. The analogue meter is good for quick diagnostic work not requiring accuracy, whereas the DMM shines when actual values are needed. The DMM doesn't care which way round the leads are, and it's digital display is unambiguous. For accurate work digital meters are less error prone. But you have to pay – very cheap analogue and very cheap digital meters are both disappointing!

Since buying a portable digital oscilloscope, I find myself using it in preference to meters. The oscilloscope is high-impedance, and accurate, and it shows what's happening over time. My previous valve and transistor oscilloscopes didn't get used in the same way because they were too heavy and time-consuming for quick dab measurements on a dining table. Same objection to my PC oscilloscope/logic analyser: though it works well it takes too long to set up for simple testing.

Horses for courses!

Dave

Edited By SillyOldDuffer on 30/12/2020 10:23:15

[Philip RoweParticipant @philiprowe13116]

Apologies for going slightly off topic, but I think relevant, what do users of Avo 8s do nowadays about the special 15volt battery that it used? I switched to DMMs probably 25 years ago because I could no longer obtain that battery. Also as others have said its too big for table top use.

Phil

[Anonymous]

Posted by Peter G. Shaw on 29/12/2020 22:26:38:

….with 1% tolerance resistors, the centre voltage could correctly be anything between 4.2v to 4.8v.

Err, with 1% resistors I think the midpoint voltage will also vary by 1%, ie, 4.455V to 4.545V.

Andrew

[V8EngParticipant @v8eng]

Posted by Philip Rowe on 30/12/2020 11:18:01:

Apologies for going slightly off topic, but I think relevant, what do users of Avo 8s do nowadays about the special 15volt battery that it used? I switched to DMMs probably 25 years ago because I could no longer obtain that battery. Also as others have said its too big for table top use.

Phil

I have an old AVO (not sure which model) have not used it for years and am sure it used a total of 3 batteries.

I think BLR154 15v Alkaline Batteries are available and advertised as replacements for the original.

Edited By V8Eng on 30/12/2020 12:22:35

[MalcParticipant @malc]

Looking in on this post I was particularly impressed with the circuit diagram produced by AJAX. Can you tell me what program was used to produce it ?

[Peter G. ShawParticipant @peterg-shaw75338]

Andrew,

I did think my calculated values were a bit out when I wrote it, but considering the time, which I hadn't realised it was, I just couldn't be bothered to check it. So thanks for the correct values.

The point I was trying to make is that digital is not necessarily the best and that an analogue meter despite its perceived lack of accuracy, is often more than plenty good enough.

I haven't done any serious electronic work for a considerable number of years now, but a bit like Dave/SOD, I do indeed have a pair of analogue meters, and a digital meter. I don't have a portable digital 'scope, but I do have a standard analogue twin channel, single timebase 'scope, and, if I can ever be bothered to mend it, a Tectronic dual channel, dual timebase 'scope. So I have more than enough test equipment available If I need them. Which I don't.

My final comment is that digital is not the be-all and end-all it's often cracked up to be.

Cheers,

Peter G. Shaw

[John HaineParticipant @johnhaine32865]

Malc there are a few free electronics packages around. I used to use DesignSpark from RS but switched a while back to KiCad. Both involve a bit of a learning curve but it's well worthwhile.

[Anonymous]

Posted by Peter G. Shaw on 30/12/2020 13:50:48:

My final comment is that digital is not the be-all and end-all it's often cracked up to be.

I'd agree with that. I have an AVO (bought from a friend mostly for old times sake) but it does sometimes get used instead of the DVM. Digital 'scopes are great in many ways, but I've seen a number of professionals get confused due to aliasing giving a misleading picture of the waveform.

Andrew

[John OlsenParticipant @johnolsen79199]

The best feature of the AVO is that you can stand on it to change a light bulb.

Even when I was using them professionally, my own analogue meter at home was 100k ohms per volt, as compared to the 20 k ohm per volt of the Avo. They were good in their day, said day being at least fifty years back. Their valve tester was quite useful too…

John

[James AlfordParticipant @jamesalford67616]

Just a quick update. Thank you for all of the advice and help.

I have replaced the BC547 transistors with the 2N2222 type. It is all working as designed now. The next step is to put it all in a box, along with the Arduino Uno, the RTC, digital display and the relays and make sure that it runs properly for a prolonged period.

Assuming that it works as hoped, the next stage is to build a mechanical clock for the relays to operate.

Regards,

James.

[pete hammondParticipant @petehammond94283]

This thread means another AVO,(now considered 'valuable' asset?) will sit on a shelf even longer- pre Christmas I had eyed up the old and dusty AVO for the cases potential to house a 180 v DC power supply for a CNC machine – a 2021 project – and recycling at its best!

Downside suitable project box now required at minimal £s and 'currently ' no car boot sales or autojumbles to shop at. full of goodies I can't 'resist'! I really find trips to the 'local dump' quite challenging so many things I could rebuild/modify or just put on a shelf!

Any alternative suggestions/donations/swaps (Watts) out there? That needs a new 'ohm' Near Aylesbury/deliverable in tier 4 times.

Happy New Year and keep safe

From 'Two AVO's ' Pete

[John HaineParticipant @johnhaine32865]

Posted by James Alford on 01/01/2021 10:05:35:

Just a quick update. Thank you for all of the advice and help.

I have replaced the BC547 transistors with the 2N2222 type. It is all working as designed now. The next step is to put it all in a box, along with the Arduino Uno, the RTC, digital display and the relays and make sure that it runs properly for a prolonged period.

Assuming that it works as hoped, the next stage is to build a mechanical clock for the relays to operate.

Regards,

James.

James, maybe a silly question, but presumably the relays will supply some sort of solenoids in the clock, in which case why not drive the solenoids directly from the transistors? What did you have in mind for the clock?

To put it in perspective the clock I described here uses a converted quartz movement as a display driven directly from the Arduino pins via a 270 ohm resistor.

[James AlfordParticipant @jamesalford67616]

Posted by pete hammond on 01/01/2021 11:06:16:

This thread means another AVO,(now considered 'valuable' asset?) will sit on a shelf even longer- pre Christmas I had eyed up the old and dusty AVO for the cases potential to house a 180 v DC power supply for a CNC machine – a 2021 project – and recycling at its best!

Downside suitable project box now required at minimal £s and 'currently ' no car boot sales or autojumbles to shop at. full of goodies I can't 'resist'! I really find trips to the 'local dump' quite challenging so many things I could rebuild/modify or just put on a shelf!

Any alternative suggestions/donations/swaps (Watts) out there? That needs a new 'ohm' Near Aylesbury/deliverable in tier 4 times.

Happy New Year and keep safe

From 'Two AVO's ' Pete

What size box do you need? I have a few odd things spare and am in Aylesbury

[pete hammondParticipant @petehammond94283]

Hello James (Sorry to others for thread drift)

Thought I was an isolated island of madness! (Near The New Zealand)

Although partly written tongue in cheek I really am looking for a box about the size of an AVO or slightly larger – think desk top PC as maximum although experience of actual PC cases is -never quite suitable..

But for COVID and my shed is COLD I would welcome you for a coffee now – hopefully sooner rather than later!

Pete

[Frances IoMParticipant @francesiom58905]

distributors such as RS or Farnell carry such boxes

also try your local Electrical trade distributor eg City electrical but several others – these often do click + collect to get over the covid closure problem – some of these boxes would look great mounted on the wall (switchbox style)

Edited By Frances IoM on 01/01/2021 14:11:16

[duncan webster 1Participant @duncanwebster1]

I got the box for my Milling Machine Table Drive from Farnells at a very good price, I think they are end of line, see my post under workshop progress 2020 August sometime

[Robert Atkinson 2Participant @robertatkinson2]

Thread drift (again) but analog meters like the AVO 8 (I have the GPO version of the SEI Selectest Super 50 which is similar) do have a couple of advanages that have not been mentioned:

They are good for assessing changing voltages because A. they average faster changes and B. your eye and brain can average slowly changing ones. DMM just give random numbers.

They are good when making manual adjustments o circuits. The visual feedback is almost immediate.

Some DMMs have bargraph displays that help in these situations but the implementaton and usefullness varies considerably, even from good manufacturers. Quite a lot of digital power meters and the Fluke 8920 TRMS digital voltmeter still have analog displays to assist with adjustments. Have more digital meter than analog but there is still a place for both in a well equipped workshop. If the only choice was the quality large scale analog like an AVO 8 / Super 50 or a cheap ebay/maplin/screwfix DMM I'd take the analog everytime.

Note as well that the midscale accuracy of the AVO / Super 8 is similar to a basic 31/2 digit DMM.

Robert G8RPI

[James AlfordParticipant @jamesalford67616]

Posted by pete hammond on 01/01/2021 13:52:54:

Hello James (Sorry to others for thread drift)

Thought I was an isolated island of madness! (Near The New Zealand)

Although partly written tongue in cheek I really am looking for a box about the size of an AVO or slightly larger – think desk top PC as maximum although experience of actual PC cases is -never quite suitable..

But for COVID and my shed is COLD I would welcome you for a coffee now – hopefully sooner rather than later!

Pete

I have sent yo a private message.

James.

[James AlfordParticipant @jamesalford67616]

Posted by John Haine on 01/01/2021 11:21:15:

Posted by James Alford on 01/01/2021 10:05:35:

Just a quick update. Thank you for all of the advice and help.

I have replaced the BC547 transistors with the 2N2222 type. It is all working as designed now. The next step is to put it all in a box, along with the Arduino Uno, the RTC, digital display and the relays and make sure that it runs properly for a prolonged period.

Assuming that it works as hoped, the next stage is to build a mechanical clock for the relays to operate.

Regards,

James.

James, maybe a silly question, but presumably the relays will supply some sort of solenoids in the clock, in which case why not drive the solenoids directly from the transistors? What did you have in mind for the clock?

To put it in perspective the clock I described here uses a converted quartz movement as a display driven directly from the Arduino pins via a 270 ohm resistor.

John.

I am a way off from starting the clock itself as I am still vacillating over the design. However, I have programmed six pins on the Uno to operate at different intervals. One will operate each second, one each minute and one each hour. A fourth will be used to strike the quarter hours, a fifth to chime the hours and the last one will mark the days. I have used a RTC to ensure that it keeps proper time and it has a LCD display to check the time.

Mechanically, there will be a lifting solenoid connected as the load on each transistor. This solenoid will pull a lever which will advance the hands, strike the hours, ring the chimes and mark the day appropriately. This stage is well in the future still.

Regards,

James.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Robert Atkinson 2 on 01/01/2021 20:57:58:

…

Note as well that the midscale accuracy of the AVO / Super 8 is similar to a basic 31/2 digit DMM.

Robert G8RPI

Out of curiosity I looked up what sort of digital multimeter you could get for the new cost of an Avo8. In 1953, the latter was advertised at £23.50, equivalent to about £660 today. (Source Richard's Radios)

Today, that money would get you a calibrated 5½ digit Siglent SD3055 Dual Display bench multimeter (DC voltage accuracy 0.015% of reading per year and 0.003% of range), plus many other goodies and change.

Not tempted – my ordinary Maplin analogue and basic 3½ meters do all I need, and I occasionally roll out the Avo too.

Dave

[John HaineParticipant @johnhaine32865]

Thanks James, so the relays are just representing the solenoids?

I don't know if you're familiar with the old Synchronome clock which used an electromagnet driven ratchet motor to operate the dial impulsing every 30 s with a very audible clunk. In the case of the observatory version it clunks every second, and every 30s too. Also the master clock clunks every 30s as the impulse is delivered to the pendulum. In my version of the Synchronome the original EM drive to the dial was instantly vetoed by the domestic authority because of the noise, so I converted the dial mech to use a small stepper motor instead to drive the minute hand. The dial is now virtually silent in operation.

This might be a point to consider – stepper motors can be cheaper than solenoids and at "clock" speeds virtually silent.

[James AlfordParticipant @jamesalford67616]

Posted by John Haine on 02/01/2021 10:44:54:

Thanks James, so the relays are just representing the solenoids?

I don't know if you're familiar with the old Synchronome clock which used an electromagnet driven ratchet motor to operate the dial impulsing every 30 s with a very audible clunk. In the case of the observatory version it clunks every second, and every 30s too. Also the master clock clunks every 30s as the impulse is delivered to the pendulum. In my version of the Synchronome the original EM drive to the dial was instantly vetoed by the domestic authority because of the noise, so I converted the dial mech to use a small stepper motor instead to drive the minute hand. The dial is now virtually silent in operation.

This might be a point to consider – stepper motors can be cheaper than solenoids and at "clock" speeds virtually silent.

John,

I confess that I have used relay and solenoid loosely. Originally, I was going to use realys, but then looked at the type of solenoid which has a sliding plunger to push or pull the mechanism. My wife's comments when I had it running with just one such solenoid made it clear that alternatives would be needed due to the noise. I have now settled on the type of solenoid which is just a round electro-magnet without any form of plunger or arm. I propose to design and build a mechanism which retains a tiny air gap between the face of the magnet and the activating arm to avoid noise.

I toyed with the idea of stepper motors, but I really like to the idea of a clock with lots of levers and arms rocking away. It might all prove to be unworkable, but I shall give it a go.

We used to have synchronised electro-mechanical clocks at the telephone exchanges where I worked. I cannot recall the make or any details, other than that they were not exactly silent.

Regards,

James.

[John HaineParticipant @johnhaine32865]

Aha! They would be PO Type 36 clocks! More details here. Very collectable these days. Based I believe on the Gents Pulsynetic system. I worked for the PO in the last days of Strowger and I guess the noise of the switching more than drowned out the noise of the clocks!

Do you mean a rotary solenoid? I have thought of using those but not found a cheap source and they don't look easy to make.

[James AlfordParticipant @jamesalford67616]

John,

Like you, I worked in the old Strowger exchanges in the later years, moving into "traffic" in 1986. They were noisy places. I am sure that my hearing was dulled by the constant racket.

This is the type of solenoid Lifting Solenoids which I plan to use. I bought one from e-Bay as an experiment and have found someone in this country selling five more unwanted solenoids for a very reasonable price.

Regards,

James.

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