Adding and analog Output to a sonometer (Feedback needed) - Page 1
Forum section: electronics / projects

author: GoatZero
author_rank: Regular Contributor
timestamp: October 07, 2013, 03:16:58 am
content: Hello, in studying electronics engineering and i happen to be taking a class called signals and vibrations, we are learning about pressure in the air and the use of the sonometter in the lab so bought one in order to use it in my experiments and proyects at home, however it didnt have an output so i could plug it to my osciloscope probes and be able use this as an output to view waveforms of detected sounds , so the plan is to add one, here i will post how i did itIm actually posting to share and this because this is the 1st proyect of this kind i make (messing with pcb) so i wanted to get any feedback about how can i upgrade or what did i do wrong or could have done betterThis might sound odd but im the only one in my entire family doing electronics and im learning from 0 everything i can from dave and at my school so i would really like to recieve some feedback and maybe any tips or warnings for the next time i do something like thisand sorry for the picture spamSo this is the sonometter, its a Sound level metter DT-854, tried looking for any kind of service manuals or esquematics online and found nothing more than more of them getting sold online it has no analog output and im about to tear it downhere you can see its gutsFor starters i started placing the probes where the transductor is however the signal was to weak, so i decided to look for an amplifier reason of why i got a piece of paper and wrote down all the ICs on sightThis is what i goti actually found 5 TL062C inside the other 3 ICs areHCF4053 (Multiplexor)http://www.datasheetarchive.com/dlmain/Databooks-4/Book615-3112.pdfHEF4013BT (Flip Flop)http://www.nxp.com/documents/data_sheet/HEF4013B.pdfOPO7C (Not sure of it )http://www.datasheetarchive.com/dl/Scans-008/Scans-00172423.pdfand 5 x TL062C OP Ampshttp://zeeman.raunvis.hi.is/~sthi/files/teaching/e2a_v2013/TL062_OP_AMP.pdfAnd then there's The Nameless Blob, which contains all the intelligence. which i felt temped to try to removeAs far as i understand the osciloscope only measures electricals signals so in theory it shouldnt cause any problems having 2 wires in pararell running out of the sonometterFor starters i started checking the VCC- (pin4) and outputs (pin1) of every IC on sightThis to try to pull a signal off one of the chips somewhere. U1 looked like a contender, i'm guessing thats a preamp for the mic, there should be an output there somewhere.I used a function generator and a speaker to set a "test tone" of 1kHz turned on the sonometer and used this to measure pins 1 and 4 of most of the AmpOPsI could have used at least 4 more hands however i ended up setting the osciloscope in acquire mode "Average"Since i needed 5 more hands and the frequency its not always being read as 1Khz by the sonometter its quite hard to read the frequency at the osciloscopeusing the average option i could get a stable reading, so i can confirm that pins 1 and 4 of U1 are the chossen ones for the analog output of the sonometeri also tried the other integrated circuits however only U1 gave me the most reliable reading compared to the other ICs, so im using itSince i found an output that matches the frequency i set, now i needed an audio 3.5mm output so i used and old Plam TX and teared it down to take the one inside to solder itonce done i had to make a cable so i could plug it in to the 3.5mm jack and then to the osciloscope so i did thisAs for the jack i had drill a hole and glue it with lots of silliconi had no other choice but to put it right below the microphone, since there was no space anywhere elseafter it cooled down i had to remove a bit since the case wasnt closing as intendedi also used thermofit so the wires didnt short anything inside, and also used a bit of silicon above the IC i soldered hoping it will help the solder to stay in placeand finally, i closed the case and lost a screw on the process so i had to look for it for 30 min on the floorafter i finally closed the case i plugged in my audio cable to my new jack and using the alligator clips that i soldered so i could plug it to my osciloscope easily , and yes i can finally can see the frequency and amplitude of the sound in my sonometer without having to open the sonometer

author: GoatZero
author_rank: Regular Contributor
timestamp: October 07, 2013, 03:25:31 am
content: Now even with the proyect/hack complete i ended up with more questions than answers (even tho i learned a lot by doing it)The osciloscope reads the amplitude (voltage) and frequency and they actually match to what i set my function generator , even when i talk it changes constantly so im asuuming its working ok, howeverHow come it can only be seen in the mV scale, why is it so small if its plugged into an Amplifier while the speaker is using a signal of 20 Vpp and 1Khz???Is there any way that the functions or reading of the sonometter will get altered by this new output in paralel?Is there a way to make sure the system is meassuring what it should meassure? (other than using the function generator)How can i make sure the reading are accurate?I was just told at school that if you use to much solder it actually acts as a capacitance, but, how much is much solder when we are soldering the pins of an IC?How can i verify is the solder i just solded is acting as a capacitance?I got really hyped when i found this proyects forum, i hope someone can help me out with these questions and im expecting some feedback and critisism if possible and thanks in advance, if anyone has any questions i will be hanging around

author: MrAureliusR
author_rank: Unknown
timestamp: October 07, 2013, 05:47:57 am
content: OP07C is another op-amp. Are you sure you wired it to the correct output amplifier? I would (personally) have done a lot more research and probing with my scope before soldering anything. You could also build a small amplifier circuit if you used low-noise op-amps to give a better signal. However if you're getting the signal across clearly on the scope then just stick with what works.

author: GoatZero
author_rank: Regular Contributor
timestamp: October 07, 2013, 07:25:23 am
content: i actually tested all the ICs and the one soldered its the one with the best output, i can easily desolder the wires i soldered thats why i put some glue above it so in case i had to move it i can do it fairly quick, however i might try i again to test the OP07C in the near future, but yes, up to now the signal i get its quite reliable but i still feel its a bit low (mV)