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A Preamplifier for Smartphone Oscilloscopes
very impressive. thumbs up
Finally, I made it :Dsorry for bombarding you with my silly questions, this is my first Op amp circuit and I am so excited about it :)I finally built the full circuit dropping the zeners and using two normal inversed-polarity leds instead of the bipolar one. I figured out the I mixed up between -ve and Gnd and I had no good understanding about the need of common, -ve and +ve for those op amps. After fixing that (and frying a jrc4558) , My problem was not the connection itself but the jrc4558 op amp which worked for a while and got fried twice for an unknown reason while measuring a square wave produced by ic555 timer (why?) !!! I replaced it with lf353N and it works ok! When I put the jrc4558 it ges very hot and it would blow(why?)Notes and Questions:0- I used a 4.7uF capacitor because I couldn't find a ceramic with this value. Is it possible to use a 470nf ceramic? What might be the effect on the circuit?1- I noticed that using the fl353N doesn't indicate the presice frequency generated by my phone, while the freq. meter on my multimeter reads 1000hz the Oscillscope pro app reads 1047 and fluctuating +-20Hz (is it really the op amp fault?)2-The wave shape changes when changing from Hi to Lo input at the same generated wave, why?3- I couldn't understand the callibration part, I measured the AC voltage of the 1000Hz sin wave from my ipad it was 0.245v , to callibrate the Oscilloscope app, where is the voltage indicated in the app? If it was the one reading delta m V then it is fluctuating so much that I can't know which is the correct value. What's missing??I would really appreciate it If you could discibe the process step by step so that my project is fully completed(thanks to you)
Ok, lets diagnose the problem.What i have done was1) I replaced the ceramic capacitor (4.7uf) with a polarized one where the posative terminal connects to the led (two parrallel leds inversed in polarities) and its negative terminal connects to the 1.5k resistor then the resistor to the negative of the battery (ground)2) I couldn't find a bipolar led so i used to normal leds in parallel each with inversed polariy meaning if enough voltage were passing one of them should be lit depending on the direction of current i guess The rest to the circuit is the same as the full circuit without the zener Diodes and the power indicator led.+ve of battery directly connects to pin8-ve of battery is connected to the ground os the circuit One Oscope testing probe is connected to the ground The other probe connects to the pot thrugh a 0.1 uf capGround of the trrs connects to ground of circuit(negative of battery)Mic line connects to the negative side of the polarized 4.7uf cap (before the resistor 1.5k)What did i do wrong and Any suggestions to fix it is appreciated
The chip should not get hot. Something is very wrong with your circuit.
Thank you chipstein, I found a 1m ohm pot today. I will start building the circuit soon and I'll update you with the results (hopefully the chip will work)
so I built the minimal circuit using the 4558d and i used a 9v battery with the same schematics but the problem is that the chip gets hot and i dont know if thats normal or not, also i replaced the 9v battery with an 11v from an adjustable ATX power source which made the chip very very hot!!Whats going on??Also, I noticed that the battery gives more cleaner signal than the atx ( connected to mains)
The 4558d is a very old chip that is listed to to need a minimum ±5 V power, so it might be marginal here. But my guess is it will be OK. The 500K pot by itself should be OK too. Good luck.
Great instructable is should say :)In my country I couldn't fine this chip , but i found 4558d JRC dual op amp.1- Is it ok to use it? what are the possible effects.2- Also, I couldn't find a 1M pot but I do have a 500K pot and many resistors, can I use a 500K resistor in series with the 500K pot to create a 1M resistance in total?
why you are used zener diod??
I think it helped. But it is also possible that there was some soldering or other technical problem on the pcb bringing higher voltage to the phone. You ware soooo right that making the circuit on the pcb can couse a lot of troubles. And I really spent so long time to find all the mistakes. A good lesson to me.But now is the device in the box and I hope it will help me with my future project. Thanks for your patient replies for our questions.
Hello, really thanks for this simple and useful project. My question: the circuit works it shows waves correctly but after some time (and sometime almost immediately) it starts dialing the last phone number. It happens so often that I can not use it. Sometime it´s necessary to restart the phone, because it tends to dial the number even after the preamp is disconnected.I have HTC 601 phone. Does anybody have such problem? Any idea what to do? But anyway, thank you a lot, if even it will not work perfectly I got a lot of important knowledges.
question why my preamp of my cellphone got been destroyed I mean it time to time the preamp overheat and pop!! And I can't use it why did just happening is there a problem with pot resistance what happen if I low resistance about 5k it will work???
what other component can I used in replace with op amp tlc 272? thank you
Hi loboat. I would like to know if you have like a page where you share your projects. I would like to contact you and ask for some help because I´m trying to know more about the way you show the signal in the phone. I would aprecciate it a lot.
Aww, that's cute. You actually think the iPhone can do more than look pretty.
what is the software for iphone?!
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