simple protection for avr transistor tester (mk-328,mk-168) - Page 1
Forum section: electronics / repair

author: crazyhog
author_rank: Regular Contributor
timestamp: September 24, 2017, 01:14:57 am
content: Today, while fixing my tek 422 scope, I forgot to discharge a capacitor before testing it with my transistor tester. I was greeted with a spark and the tester is dead. This is the second one I lost this way. Very annoying.Here is my idea for a simple protection mechanism.1. add anormally closedmomentary switch to the tester that shorts the 3 input pins together.2. test setup: connect the DUT to the input pins. since the momentary switch is normally close, the DUT automatically discharges.3. test: first press and hold the momentary switch to break the shorting of the 3 pin. than tap the test button. keep pressing the momentary switch until the tester is done. If the operator forgets to hold down the momentary switch, the tester will simply fail and no harm will be done.Basically, this always automatically discharges the DUT before testing. The use of the tester becomes a two finger affair.What do you guys think? Any other clever and, importantly, simple solutions?

author: stj
author_rank: Super Contributor
timestamp: September 24, 2017, 06:16:16 am
content: a discharge relay is already in the original design - go look at the pdf.

author: crazyhog
author_rank: Regular Contributor
timestamp: September 24, 2017, 08:03:51 am
content: I already thought about the relay idea. Frankly, it is the obvious solution, a pedestrian solutionIt's similar to the Peak Atlas ESR meter solution.I felt it can be done even simpler as I've presented. I also want a simple solution that the many existing owners can easily retrofit their devices.By the way, my solution will protect the tester even when the battery is too low to operate the relay. Will the discharge relay in the original design still protect the device when the battery is low? Which solution is more robust?

author: Gyro
author_rank: Super Contributor
timestamp: September 24, 2017, 09:00:08 am
content: I retrofitted one to my T4 version.QuoteYes, it's a normally-closed relay, it only opens for the duration of the test. If there isn't sufficient battery power, it will never open.

author: crazyhog
author_rank: Regular Contributor
timestamp: September 24, 2017, 10:41:33 am
content: Gyro,Thanks for the feedback. Does the retrofit require reprogramming the firmware? Is it possible to retrofit all variants of the tester old and new? I don't have the equipment nor the inclination to acquire these firmware stuff just for this purpose.So it boils down to using my finger to operate a switch or a relay to operate a switch. Using two of my fingers seems quite alright. Besides, relay requires activation and holding current which will drain battery faster. I wonder if the relay's holding current is larger than the test current; probably true for most tests. Probably cut battery life by more than half.Anyway, different approaches are fine. I was aware of the relay solution and I am just unimpressed with it. I am however interested to learn if others have come up with smarter solutions.

author: Gyro
author_rank: Super Contributor
timestamp: September 24, 2017, 11:29:16 am
content: No, the retrofit doesn't require any different firmware (as far as I'm aware anyway) It requires a transistor controlled by the same pin that the external reference is connected to - As stj says, it's all documented in the PDF.The holding current, of course dependent on the choice of relay but will be an additional drain briefly during test regardless.It comes down to automatic vs manual, and the availability of a suitable double pole breaking push button. Individual choice.

author: crazyhog
author_rank: Regular Contributor
timestamp: September 25, 2017, 09:19:59 am
content: Hahah! My interest has been piqued! I found some interesting stuff in the firmware and I also have another idea to further enhance my enhancement and ultimately improve the tester project!First things first, bad GyroYou're BS'ing me!As expected, the relay protection code is in the current source code trunk. Just search for the TPRELAY macro in the source. However, if you go back 2 versions (2 years ago) and look at ttester_111k, that code doesn't exists. Many manufacturers are behind on using latest firmware and they also modify them heavily. So no, many existing tester cannot be upgraded without new firmware.Stepping back, a quick disclaimer, I did not want to waste time on the boring relay solution, therefore I did not look at the code carefully. In the event the macro was rename, I will stand corrected!Here is the source of all the releases going back 5 years.https://www.mikrocontroller.net/svnbrowser/transistortester/Software/tags/Back to my original enhancement idea, I did a bit more research and thinking and made good progress!First, I found a 3PDT (9pin) momentary switch on ebay!http://www.ebay.com/itm/ST9P02LB-3PDT-9Pin-Guitar-Effects-Pedal-Footswitch-Momentary-Switch-AC-125V-4A-/322653255134?hash=item4b1fa1f5de:g:tXUAAOSwOfdZuv7fI needed only 2 poles to short the 3 input pins together. I still have the 3rd pole that can be use as the test button!Yup! It is possible to operate the tester with 1 fingers and have auto DUT discharge and tester protection! Just one button click and I can break the shorting of the 3 input pin and start the test!Hon hon hon, unfortunately not so easy mon ami! I wasn't sure how the firmware was trapping for the button event to start the test cycle so I needed to take a quick look at the code first. On a side note Gyro, this was the main reason I looked at the code. I kind of already knew you were BS'ing me when I read your reply.What I found is the tester actually distinguish between short click and long click will run in different modes!So my latest idea to implement a single button click solution may need a simple firmware change for newer testers (also maybe not! TBD). All the existing relay firmware code and the relay circuit can be tossed into the trash bin. No need to waste half or more of the battery on operating the relay. Simpler circuit, simpler code, and higher battery efficiency!For owners of older testers, I suspect the old firmware will work with the 3PDT button unmodified as describe above since they don't have the new features that could get in the way.And for those who want a guaranteed solution for all testers, new and old, ebay to the rescue! Just use my original enhancement idea with a DPDT momentary switch and perhaps 10 minutes of rewiring of the input pins to it.http://www.ebay.com/itm/Red-6-Pin-DPDT-ON-ON-Momentary-Push-Button-Switch-AC-125V-5A-250V-2A-/232276845587?hash=item3614c76413:g:YRYAAOSwv0tVfYW2And use your 2 fingers! For those who don't even want to lift 2 fingers; well use your noggin to come up with something more clever!Kidding aside, I have a new tester on order. It will take a month to get it in my hand. After I work out the kinks I'll contribute this back to AVR tester. I really like this tester and it will please me a lot that a community solution is superior in every way to the commercial solution.

author: madires
author_rank: Super Contributor
timestamp: September 25, 2017, 09:44:54 am
content: Some users put a small piece of PCB in front of the test pins for discharging caps. Very simple and cheap. Bonus points for making two pads and placing a resistor in between

author: crazyhog
author_rank: Regular Contributor
timestamp: September 25, 2017, 10:03:41 am
content: Ahmi amigomein Freund, the low rent solution!I play with electronics for fun. If I should ever find myself roughing it with low rent solutions instead of enjoying the creative journey I should be ready to change my hobby to pushing daisies!http://www.urbandictionary.com/define.php?term=pushing%20daisies

author: CJay
author_rank: Super Contributor
timestamp: September 25, 2017, 12:20:37 pm
content: Quote from: crazyhog on September 25, 2017, 10:03:41 amPfft, sometimes the low rent solution is the very best solution because it frees you up to play with the more interesting things, a realisation of age is that there is only so much time to spend on the boring stuff in this life before daisies become the only use you can be put to

author: crazyhog
author_rank: Regular Contributor
timestamp: September 25, 2017, 03:04:43 pm
content: Hi CJay,You have a good point. However, there are 2 big elephants in the room you neglect to address.Problem 1:There should be some minimum standards before one present something as a good solution to othersIn general lose components don't have a large charge, exceptions not withstanding. In this case, the little PCB in front of the test pin adds minimal value. Both of my testers were destroyed while I was doing in circuit testing. The machine was power off but I forgot to discharge all the caps. This is the most common situation. In this scenario, to use that little PCB to discharge the DUT in circuit is cumbersome indeed! Just use a test lead.The PCB has a small redeeming value, it does provide a reminder that the DUT should be discharged. However, can this task not be much more efficiently accomplished with a label tape to the tester? Frankly, wouldn't you agree the PCB approach is actually worse than a label because it is too complex for what it does in comparison?And what are we if we don't have standards? We are just a bunch of filthy animals!Problem 2:Routinely, we cobble together quick and dirty solutions because we have competing priorities (CJay, this is your more interesting things argument). This absolutely fine! But to argue a quick and dirty effort as a good solution you are just fooling yourself and others, o' chap! Intellectual honesty good, CJay badWe have commercial solutions and community base solution all pursuing the goal of solving the one component that fails the most: the human operator! The low rent PCB approach is not a solution; never mind good!

author: CJay
author_rank: Super Contributor
timestamp: September 25, 2017, 03:33:42 pm
content: Quote from: crazyhog on September 25, 2017, 03:04:43 pmMy apologies, my myopic old eyes missed the bit where you said it was in circuit, indeed, I looked again and couldn't find it at all so the solution was valid right up until you threw in that, to suggest I'm being intellectually dishonest is, in my opinion, insulting so I'll refrain from commenting on your posts in future, enjoy your solution hunting.

author: crazyhog
author_rank: Regular Contributor
timestamp: September 25, 2017, 04:19:38 pm
content: CJay, my apologies if I touched a nerve. But... you are still arguing the PCB approach is valid actually supports my point!Allow me to broad stroke this and see if I am fair:- I analyze the PCB approach covering different usages. Wouldn't you agree it is right to analysis different usages?- I've shown "out of circuit" a label tape to tester to remind the user works better- I've shown "in circuit" a test lead works better- Most importantly I argue the PCB is not a solution because it doesn't properly address human frailty! The PCB is counter to other efforts by the industry and the community.You couldn't point out flaws in my analysis. Yet, you stick to your claim.Touchy feelings trumpsfacts and logic?What is intellectual honesty?I stand ready to be corrected. I also like to thank those that point out my errors.And o' chap, what's up with the thin skin?! Your problem is definitely not your eyes

author: stj
author_rank: Super Contributor
timestamp: September 25, 2017, 05:42:26 pm
content: i dont know why you are doing this yet,the first "upgrade" should always be a 6 or 10way programming header.then a 16MHz crystal.