(25-07-2011, 02:49 PM)martyb123 Wrote: [ -> ]spose ill have to work out how to take the plastic face off my meter without breaking it to get the label on it i,m thinking thats not possible?? or spose they sell meters with removable faces???? youv,e really got me curious now can i not just leave it alone???
Th meter I used was from ESR Electronics - a UK company, and cost about £7.00 GBP inc Tax - about $12 AUS. Jaycar in Oz sell something similar, but it costs a lot more - $17.95 - about £11.00GBP. CAT. NO. QP5012. See here:
http://www.jaycar.com.au/productResults.asp?MID=1&SSUBID=565&SUBCATID=948&keyform=CAT2#1
http://www.jaycar.com.au/ShowLargephoto.asp?id=5337&PRODNAME=0 - 50uA MU45 Panel Meter - Moving Coil Type&IMAGE=
The clear plastic meter cover of such meters can usually be carefully prised off, then, as often as not, the scale plate is held on with two small screws. I just removed the scale plate, being careful not to damage the meter needle, turned the scale plate over, and - having printed the scale of satin photo paper, stuck it to what was the back of the scale plate, then re-assembled it.
If a meter can't be dismantled, the best thing to do is to infer the ESR from the 50uA scale, which will be in divisions of 10 from 0 to 50. 50 is of course FSD, so is zero Ohms, 40uA, is about 4 Ohms, (80% FSD), 25uA is about 10 Ohms, and 10uA is about 20 Ohms. In practice, anything with an ESR much above 4 - 5 Ohms is suspect and should be compared with a known good new one - not NOS.
Hope that helps a bit.
David
my meter was $6.50 out of hong kong and i thought that was enough to pay. my schematic does have a 22k potentiometer but it does not have the r17 resistor fitted so maybe it does need the 22k pot will not know until i get this finished as to wether it needs that resistor or not depending on the meter used as you said earlierso i have 20 k 25 k and 50 k pot to try in this circuit as i,m thinking resistor 17 was put in place to compensate for the pot size being small in the first place and thah r17 resistor was added to the pot to give it more resisatance???
i do now have the 22k pot also to try with my schematic and have given you the schematic updated version of the original idea so you can now see what i,m building
(26-07-2011, 03:13 AM)martyb123 Wrote: [ -> ]my meter was $6.50 out of hong kong and i thought that was enough to pay. my schematic does have a 22k potentiometer but it does not have the r17 resistor fitted so maybe it does need the 22k pot will not know until i get this finished as to wether it needs that resistor or not depending on the meter used as you said earlierso i have 20 k 25 k and 50 k pot to try in this circuit as i,m thinking resistor 17 was put in place to compensate for the pot size being small in the first place and thah r17 resistor was added to the pot to give it more resisatance???
i do now have the 22k pot also to try with my schematic and have given you the schematic updated version of the original idea so you can now see what i,m building
Hi Marty,
Thanks for posting the updated schematic, which simplifies things compared to the original, and I note the added 100nF cap (C8) on the input to the 7805, which is an easy mod. It can be added across the tracks of any existing boards if problems are experienced, and I'll update the PCB track layout to add a couple of pads for C8 for any future builds.
I think you may be right about R17 - the only thing I can assume was that it was to obviate the risk of damaging the meter needle if the 22k pot was turned to minmum resistance, as when the prods werre touched together, the needle could end stop. R17 would limit the risk of that. However, the einsible thing to do when setting up the meter would be to set the pot to maximum resistance then with the prods shorted together, to reduce the resistance to get FSD on the meter. If it's a preset pot on the PCB, once set, there's no risk of inadvertently tweaking it, as their would be if it were on the front panel.
Your meter was cheap enough - where would we be without internet!
Have fun,
David
the pot on the front panel was there to make it easy to set the fsd on the meter before you started to use it to test caps so if you put in the drawer for a year you would need to get to that pot knob to re-adjust the fsd before you used it again just incase the 9 volt batery had dropped significantly whilst in storage so he must of been thinking that he would need easy access to that pot for adjustment and probably a lot of other people would of thought the same as him, mind you it may not ever need adjustment so what you have done by placing it inside also works just as well so it gets down to personal choice. is my schematic was missing the second capacitor i would have been questioning further over why it was missing before i went and ordered the parts to build it.mind you lots of circuits will function quite well with parts missing which are not crucial to its operation in this case, bear in mind that circuit diagrams uploaded to the internet are not always complete as the designer of the circuit assumes that for example pin 14 and pin 7 of ic,s are for the positive and negative but are not always drawn in, sso forums are neede to discuss whats missing or incomplete or setup wrong or 1 wire on the schematic is drawn the wrong way in there cad program, human error factor is always there.and bill gates famous words were (thats a good upgrade) as he always looked for improvment on what he had thus making his company so successful.
(26-07-2011, 10:00 AM)martyb123 Wrote: [ -> ]the pot on the front panel was there to make it easy to set the fsd on the meter before you started to use it to test caps so if you put in the drawer for a year you would need to get to that pot knob to re-adjust the fsd before you used it again just incase the 9 volt batery had dropped significantly whilst in storage
The original designer never ran it off a 9V battery Marty - only four nicads, which - whether the meter was used or not - would self-discharge in a couple of months or so, never mind about year. And he never had any voltage stabilisation, which is why he said in his update in SEPT 2009: 'The zero of the meter tends to drift with changes in voltage'. Hence he needed a a front-panel control to tweak it for FSD as the voltage dropped over time. Fitting a voltage regulator obviates the need fo a front panel control - if FSD cannot be achieved it means the P3 battery has run down!
I think we've probably exhausted any useful coversation on this now, but when I've updated the PCB track layout to include 'C8', Ill post the amended artwork on the forum, should ayone wish to build th project.
Thanks for your valued input Marty, and best of luck with your meter.
David
Hi,
It seems ages ago that David very kindly gave me one of his excellent populated ESR boards. As David had already done most of the work I thought it would be an easy matter to make a wooden box and connect everything up.
How wrong I was; I made the wooden box very easily using the home made router comb jointing jig which David also kindly supplied the plans for. Then it all went downhill; I'm no whiz kid at electronics and every time I sat at the bench to work on this I got called away for something or other; I ended up zapping components making this into a much bigger job.
The harder I tried the worse it all became so last night armed with a lot more information David had sent me I decided once and for all to either get it working or destroy it because frustration had set in. I asked Bron to tell anyone wanting me to say I was on another planet.
I had bought a supply of 5V regulators; chips and transistors. I had already replaced the regulator so knew the supply was OK. Ten minutes into the job the instrument was working. Like a fool I had managed to install the transistor the wrong way around; a new transistor installed correctly fired the meter up much to my relief.
Whilst sitting in the waiting room at the hospital I was reading "Fault- finding Electronic Projects" by R.A.Penfold and read the article on making an SCR (Thyristor) tester. This appeared simple enough so I've taken the liberty of adding it to this ESR making it two instruments in the same box. All it needs now is the crocodile clips adding then it is completed.
I added a plug and socket (Jack) so that I could power from a battery as shown or use one of my power supplies.
I can't thank David enough for his generosity and I know I'm not the only one to benefit greatly by knowing David; genuine friends like David are very rare to find these days. Thank you David for all your help; I hope I can respond in kind.
Kind regards, Col.
[attachment=2753]
Thanks for your kind words Colin - making the PCB was a small gesture to repay all the help that you've given me, which is what the forum is all about I guess. Without your help and encouragement, my little Lorch lathe would still be a rusty heap, languishing neglected under the bench where it's been for the last five years!
Glad to hear that the ESR meter is now behaving itself. In the ones that I've built, I've used the metal cased 2N2222A transistor, and though I explained the pinouts and provided a diagram of the plastic ones that some constructors have used, I didn't build one using a plastic cased transistor to show the correct orientation on the PCB.
However, I've now made a couple of mods to the PCB layout based on feedback.
Firstly, though I know of no cases of the voltage regulator misbehaving, nevertheless, it's good practice to include a cap on the input side of the regulator, as forum member 'MartyB' pointed out recently. This can easily be done as a retro mod, simply by drilling through the +VE track and the ground track on the input to the regulator with a 0.8mm drill, and soldering a 0.1uF cap across the tracks, or more simply, to add the cap underneath the PCB, soldered on the two tracks. However, I suspect that most who have built the meter and found that it works well, will want to leave it alone! On the amended PCB, I've added a couple of pads for this addtional cap.
Secondly, it's become common practice of most magazine projects - Everyday Practical Electronics, 'Silicon Chip' etc (from whence, many EPE designs originate, in Oz), to include what's often unkindly referred to as an 'idiot diode'. This prevents damage or destruction of equipment due to inadvertent reversal of polarity. I know that a lot of contructors prefer to power bits of test gear with 'wall warts' rather than to fit batteries in everything, but personally, with something like an ESR meter, which is used only intermittently, and then only for a few minutes at most, I just use a cheapo PP3.
The problem with wall warts is that there's no one convention as to whther the centre pin is +VE or 0VE. Thus, it's easy to inadvertently apply reversed polarity to equipment. Some manufacturers recognise this risk and fit a reverse protection diode - others don't. With 1N4001s costing only a penny or two, at least if we home-brew, we can build things up to a standard - not down to a price, so I've amended the track to allow a protection diode to be fitted on the input to the voltage regulator. When I've etched and built a PCB up and tested it to confirm these mods are satisfactory, I'll post the amendments on the forum, with updated artwork, and an annotated layout showing all of the mods from the original version. I'll also use a plastic transistor and post a photo of a made up PCB to show the correct orientation.
As an aside, while writing on the topic of protection diodes, my son has several Roberts Revivals, which look presentable enough on the outside and have sold well - indeed, they've been such a money spinner that they revived the company's fortunes. But on closer inspection, they're really quite tatty inside, with their poorly put together MDF cabinet and puny speaker, and worse still, they have no reverse polarity protection. Personally, I think this is dire on a radio that's touted as a quality product at a ludicrously high price. Robert's 'get-out' when a radio is smoked due to polarity reversal will be in their instructions - 'always use the correct power supply'. My son always does, but indvertently plugged in the wrong lead - one that serves his i-pod docking station, next to his Revival. A puff of smoke, and that was it.
Not holding out much hope, I said I'd have a poke around, but found that the Revival PCB is unrecognisable as a radio at all. It has no IFTS no oscilator coil, no transistors and only three ICs - one is the audio chip, another takes care of AM, and the other, FM. The audio chip was clearly burnt to blazes, and an electrolytic cap with it. The chip is now obsolete, but I managed to get one quite cheaply from the States. That restored the radio on FM, but the AM chip was also jiggered - two rows of 28 pins! He never uses the radio on AM, so he was content with that, and I decided to quit while I was winning.
Roberts have always had this propensity to do quirky things - the ghaslty Mullard Modules, the TAD100 IC, and now this malarky. There's a saying in Yorkshire - 'all fur coat, but no knickers' - a term of disdain for those who haughtily put on airs and graces, (Think Hyancynth Bouquet!). In more polite circles, the term that tends to be used is 'mutton dressed up as lamb'. I'd say that leaving a 1p diode out of a £150 radio fits either description nicely. Nothing at all to do with ESR meters - just an example of what happens when a simple protection device isn't fitted.
Rant over.
If anyone on the forum decides to have a go at building the ESR meter, if they get stuck and can't get it to work, I'll be happy to help. The layout is uncritcal - it can be built on stripboard as well as a PCB. For anyone who has a scope, it makes a nice project to get to know how to use the scope.
It has to be said that for valve radio restoration, an ESR meter has little application. Most valve radio only have three electrolytic caps - two for smoothing, and one for the cathode bypass in the audio stage - as often as not, a 25uF 25V, which I routinely replace as they're almost always shot.
However, transistor radios often use several small electrolytic caps, and given their age (R200s, TR82s etc) they will often have a high ESR. They may not stop the radio from working, but they will degrade its performance. On the other hand, when checked on an ESR meter they ma be fine, so can be left in place, rather than to do as we tend to with waxy caps in valve radios and pull them out, come what may.
David
(06-08-2011, 08:36 PM)Yorkie Wrote: [ -> ]Roberts have always had this propensity to do quirky things - the ghaslty Mullard Modules, the TAD100 IC, and now this malarky.
Not those nice little metal boxes that we had so much fun with replacing the AF115 & AF117's David? I did so enjoy unsoldering all those wires connected to the band selector switches. One of those 5 minute jobs!
Most of the quality went out of the window with Robert's when the family sold out to Glen industries (Morphy Richards, Dimplex etc.) The radio's were then all imported. I remember Robert's reps. were always very smart and professional back in the 60's.
Roger.
I‘m afraid that the amount of information imparted in previous posts may have made this useful little project seem rather more complicated than it is. In the transition of the forum from ‘GF1’ to ‘GF2’ the pictures and PCB artwork have been lost from the thread, without which there is insufficient info for anyone who might be contemplating building the project. Furthermore, based on feedback that I’ve received, I felt that two slight amendments to the design were called for:
Firstly, the addition of a 0.1uF capacitor on the input to the 78L05 voltage regulator, which is considered good practice, though I’ve had no indication from anyone that the lack of this capacitor has caused any problems.
Secondly, the addition of what is often (perhaps unkindly!) referred to as an ‘idiot diode’ to protect the meter from accidental polarity reversal should a constructor decide to use a ‘wall wart’ to power the unit rather than a PP3 9V battery. I don’t personally see the need to use a wall wart as the meter is only used occasionally and for a few minutes, and draws only a few mA is use. It only requires a 5V supply, via the TL805, so a PP3 can drop by a few Volts before it ceases to power the unit correctly. That said, it is a fact that some constructors prefer to use a wall wart, and have inadvertently reversed the polarity, which will destroy the TL805, the 74HC14N IC and 2N2222A transistor. Not the end of the world – all three will cost no more than a pound in total, but the addition of a protection diode – a 1N4007 say, costing just a few pence, will obviate the risk. (Such diodes are now routinely incuded in all designs in Everyday Practical Electronics).
I’ve therefore modified the PCB artwork to incorporate these two additions, and also have highlighted the differences of the component layout as compared to the original. In other respects, the component layout is as per the original project.
I also found a source of a larger 50uA meter – the original 50uA meter from ESR Electronics Ltd was 60mm x 45mm, but I’ve found that Rapid Electronics stock one at a similar price which is larger (70mm x 60m) and hence, the dial is less cramped and clearer to read. With my limited artwork skills, I’ve managed to enlarge and re-calibrate the dial to suit this meter. The dial can be printed onto photo paper, and if the scale-plate of the meter is carefully removed, can be stuck on the rear of the plate and the plate fitted back again. Removal of the dial only involves two crews, and the scale-plate, another two crews.
Some constructors have found difficulty in obtaining the 0.47uF 400V capacitor ‘C5’ which is the ‘DC isolation capacitor’ that protects the meter should it be inadvertently applied to a charged capacitor. Such capacitors come in various case styles with both axial and radial leads. I’ve therefore amended the layout of the connectors points at the RH end of this cap on the PCB, with three holes as options for different sizes. (The overlay mentions just two, but the PCB has three options). The polyester capacitor that I use is available from Rapid at 38p.
To ensure that the new layout is satisfactory, I’ve built a meter and have attached a few pictures which show the meter and a close-up of the PCB. I’ve also attached a pic of the PCB artwork, the component overlay highlighting where it differs from the original designer’s layout, and a copy of the updated dial artwork.
The link to the Rapid 50uA 70mm x 60mm meter is here:
http://www.rapidonline.com/SearchResults...kw=48-0300
The link to the 0.47uF 400V capacitor is here:
http://www.rapidonline.com/SearchResults...kw=48-0300
I should add that for those who aren’t equipped to make PCBs, the layout isn’t in any way critical and could be built on ‘perf-board’ using a similar layout, connecting component wires beneath the board. Not perhaps as neat as a PCB, but nevertheless, functional. In earlier posts I’ve covered in depth the construction, testing, troubleshooting and use of the meter, but if anyone does build it and have trouble getting it to work, I’ll be happy to help.
All of the components apart from the optional LED, the switch, battery and meter, are now mounted on the PCB, with four pairs of pins for connections – two for the battery, two for the meter, two for the cap test leads, and two for the LED. When built, the only adjustment needed to set up the meter is to temporarily short out the cap test leads and adjust the pre-set pot on the PCB to get full scale deflection. (Meter needle to the far right of the dial). As with an analogue Ohm-meter, the dial reads from right to left – lowest readings to the right – higher readings to the left.
I know that several forum members have these meters, and I hope these notes might encourage a few others who like home-brewing to have a go at building this cheap but useful little item of test gear.