Video is not the best format in which to present schematics and programming code so I have prepared a companion PDF file which contains that info as a permanent record. You can view and/or down load from here: s3-us-west-1.amazonaws.com/hmt-forum/tony_foale_hardness_tester.pdf ********** Important notice ************** I made an error in the two schematics. The IR LEDs and the power LED are shown around the wrong way. I showed the anodes at the bottom, they should at the top and the cathodes at the bottom. ****************************************** The Arduino code can be copied and pasted in text form from here: www.homemadetools.net/forum/everyone-needs-hardness-tester-83780#post175021
Hello Tony, Thanks for these two videos... I have no knowledge of electronic but this has wetted my appetite to have a go as this would be such a useful tool... many thanks for sharing. Take care. Paul,,
Nice. So now you have me thinking. This should be on the to build list. It will prove a useful addition to my shop. Just have to do a little more thinking.
Very nice work Tony and it's obviously working well, but just on a technical point, the comparators are not acting as Schmitt gates, just simple level detectors. You have no positive feedback to add hysteresis.
Wow, that is ingenius. I’ve been looking for hardness tester but they are all very expensive. I’ve had my eyes on Leeb testers. Commercial ones seem to have also spring so they can be used in any position. However that is not a good thing as there is one more variable in the equation to mess up the readings. Who needs to measure awkward positions anyway? Your free fall design is very simple and there really are no things that could go wrong. Even your code is utilizing KISS method as its finest. Brilliant. I was thinking of making my own version using PIC micro as I’m familiar with it but “micros()” function from Arduino alone is enough to dump that idea. With PIC I’d have had to rely on timers which would have made it more complicated and maybe not that reliable. I’ve got a question, why did you use in the code distance between sensors 4.9mm? Was it to compensate something or was the distance actually that and not 5mm? Also what was the centerline distance from the lowest sensor to the bottom of the tube? 7.5mm? Thank you for sharing this.
Offhand I do not recall why I used 4.9mm I suspect that was the result of actual measurement after it was built. The distance at the bottom just needs to be just a tad more than the diameter of the ball.
Hi Tony, Great project. Thanks so much for sharing the in-depth information required to build one. All the machining I have covered, but I have extremely limited knowledge when it comes to electronics. Would a Texas Instruments LM393N/NOPB still do the job? And there are many IR photo transistors options, will they all do the same job for this project? These are probably extremely basic questions, but I don’t want to make any mistakes. Thanks once again. Alan (Australia)
Any chip labelled LM393 will do the job. I think that the only significant difference is in the chip packaging. If you are ill equipped for electronics work you should avoid modern tiny surface mount devices. These are not easy to solder unless you have the right setup. As for the sensors, it will be easier for you to use a combined unit. I searched Amazon for HY860H-A and up they came. Just stack 2 on top of one another
Could you please explain how you calculated the 2as(twoas) constant. Seems to me as this was used as a means for calibration of the unit and one would need to be able to calculate it in order to reproduce this machine and account for minor variations.
a is gravitational acceleration = 9.807, s is the remaining distance to fall after the ball passes the midpoint of the timing section = 9.25 mm or 0.00925 m. So 2as = 2 * 9.807 * 0.00925 = 0.18143
To add to the reply. 2as = (dV)^2 or the square of the velocity change which can be added to the measured velocity like V =sqrt (Vm^2 + 2as) which is done farther down the code, where V is impact velocity and Vm is measured velocity. For the dimensions of my device it makes close to 1% difference in the impact velocity compared to the measured velocity 9.25 mm above the impact zone.
