Mirror Camera project

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Re: Mirror Camera project

Postby gary » Sat Jul 05, 2014 10:54 pm

Very poor frequency response both lower and upper - can you post a block diagram of the signal path showing what each section is doing please?
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Re: Mirror Camera project

Postby Harry Dalek » Sat Jul 05, 2014 11:53 pm

gary wrote:Very poor frequency response both lower and upper - can you post a block diagram of the signal path showing what each section is doing please?


OK Gary heres a drawing hope it makes sense the only difference from the photo diode test to the solar cells was no head amp just solar cell direct to the laptops input.

I had them at a slight distance apart but don't think i did any thing different to the flying spot sweep test many moons ago .

Also then the solar cell had a head amp for that test.

Yesterday the test was worse ...sounds like the photo diode is not great or i have done something wrong .
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Re: Mirror Camera project

Postby gary » Sun Jul 06, 2014 12:04 am

Ok, so it seems it could only be the head amp causing the low and high freq roll off.

I am not happy with the phone/mp3 source but, and correct me if I am wrong, that is what you were using in the previous tests right? (i.e. direct from phone to laptop) and that seemed fine. I suppose the only test you didn't do then is with the sweep - perhaps you should back up and do that before looking at the head amp.
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Re: Mirror Camera project

Postby Harry Dalek » Sun Jul 06, 2014 11:47 am

gary wrote:Ok, so it seems it could only be the head amp causing the low and high freq roll off.

I am not happy with the phone/mp3 source but, and correct me if I am wrong, that is what you were using in the previous tests right? (i.e. direct from phone to laptop) and that seemed fine. I suppose the only test you didn't do then is with the sweep - perhaps you should back up and do that before looking at the head amp.


OK Gary so its better if it were a Wav file ?

I have to say no I think i used a second lap top when i did the flying spot head amp test ,i was thinking more the basic idea of the test ...

But i do have the same head amp used back then as a control test if need be .

I also recall i didn't use a transistor circuit as this time as the laptop i used was enough to light and modulate the led.

Gary i see your way of thinking your more precise in your testing approach,i will just take this in and have another look .

Btw because the solar cells had no head amp did you notice a difference ? i don't have any thing to view a recorded wav as i do live one and i didn't see how they went i just recorded them .

I will do a phone to laptop direct cable sweep as you mentioned that will see test the phone ,i sort of did that with an nbtv wav when i started the testing but it would show how well it does it via a frequency sweep.
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Re: Mirror Camera project

Postby gary » Sun Jul 06, 2014 1:42 pm

Yes Harry, mp3s are not a good choice for video - the compression is done at the expense of audio we don't hear - but when we convert it to video we very definitely see it.

It is not so much using .wav files as they can in fact be mp3 encoded as well - what you want is PCM (i.e. no compression) - thankfully nearly all .wav files are.

Harry I strongly recommend that you download and install Audacity - it is totally free and will give you everything you need to analyse the audio files.

In addition, when recording these tests always record in mono 48kHz if possible.

Harry could you also post the sweep file as well? so we have a benchmark.

The secret to testing and debugging is to minimise your variables - ideally only change one thing at a time.
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largesolarcell.jpg
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little solarcell.jpg
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photodiode test 2.jpg
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photodiode test 1.jpg
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Re: Mirror Camera project

Postby Harry Dalek » Sun Jul 06, 2014 2:03 pm

Hi Gary

Just a quick one before i review in your last post .

It looks like i have lost the original sweep its not one my old laptop ,i was just doing another one ,but it might be best if i do get a good one via you before i go on testing.
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Re: Mirror Camera project

Postby gary » Sun Jul 06, 2014 2:21 pm

Harry Dalek wrote:Hi Gary

Just a quick one before i review in your last post .

It looks like i have lost the original sweep its not one my old laptop ,i was just doing another one ,but it might be best if i do get a good one via you before i go on testing.
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Re: Mirror Camera project

Postby Steve Anderson » Sun Jul 06, 2014 2:46 pm

Suggestion - if you're wary of the original mp3 sweep file, as Gary suggests install Audacity. Within it you can generate sine-wave tones across the audio band, though I don't think a sweep. Say at 1kHz, 1.5kHz, 2.2 etc, much as the spacing of resistor values, edit these step-tones together, 30secs of 1kHz as a line-up, then say 10secs of the others. I think the highest it will generate is 20kHz - enough for NBTV.

Make sure that they are displayed at equal levels in Audacity then check the output of the phone/laptop/whatever is the same - you could well be surprised, especially with a phone!

When you measure do not use an AC multi-meter, most give up at 1kHz or less, especially the digital ones, use a scope. They are mainly intended to just measure AC mains frequencies, not full-band audio. (Exceptions - expensive Flukes). Make sure your test set-up isn't feeding you duff info...

Steve A.
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Re: Mirror Camera project

Postby Harry Dalek » Sun Jul 06, 2014 2:53 pm

gary wrote:Yes Harry, mp3s are not a good choice for video - the compression is done at the expense of audio we don't hear - but when we convert it to video we very definitely see it.


Oh i see that was a problem....

It is not so much using .wav files as they can in fact be mp3 encoded as well - what you want is PCM (i.e. no compression) - thankfully nearly all .wav files are.


Will keep to wav files from now on,
Thanks for up loading the sweep that will make it easier a factor i know is correct .

Harry I strongly recommend that you download and install Audacity - it is totally free and will give you everything you need to analyse the audio files.


I will down load that i was just using NCH tone generator but that one sounds good ...

In addition, when recording these tests always record in mono 48kHz if possible.

Harry could you also post the sweep file as well? so we have a benchmark.

The secret to testing and debugging is to minimise your variables - ideally only change one thing at a time.


I do try to test as i go ,but on the head amp side of things i know i have not tested it fully ,i understand the band width sweep ,but i have never heard of a correct way to test the light sensitivity part ...i have tried little experiments on how low a light level it can pick up at night with reflections but nothing really i could put a number to .

Thanks for the test results screen Gary !
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Mirror Camera project

Postby Harry Dalek » Sun Jul 06, 2014 3:52 pm

Steve Anderson wrote:Suggestion - if you're wary of the original mp3 sweep file, as Gary suggests install Audacity. Within it you can generate sine-wave tones across the audio band, though I don't think a sweep. Say at 1kHz, 1.5kHz, 2.2 etc, much as the spacing of resistor values, edit these step-tones together, 30secs of 1kHz as a line-up, then say 10secs of the others. I think the highest it will generate is 20kHz - enough for NBTV.

Make sure that they are displayed at equal levels in Audacity then check the output of the phone/laptop/whatever is the same - you could well be surprised, especially with a phone!

When you measure do not use an AC multi-meter, most give up at 1kHz or less, especially the digital ones, use a scope. They are mainly intended to just measure AC mains frequencies, not full-band audio. (Exceptions - expensive Flukes). Make sure your test set-up isn't feeding you duff info...

Steve A.


Hi Steve

Just been using Gary's wav file to test both my phones as a frequency sweep play back device just to see which one is doing a better job.

So i have tested here direct connections of the iphone and samsung to my toshiba lap top ,i used power sound editor to record the tests at 48khz mono .

I will play around with Audacity when i download it later today.

You can both have a look at the test below ,i sort of think with out lining them up the iphone did better ?
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iphonetolaptop.wav
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Mirror Camera project

Postby gary » Sun Jul 06, 2014 4:34 pm

Harry both of your files are still 44.1kHz stereo - so you are doing something wrong when recording.

Here are the response graphs - as you can see the samsung appears to be far superior in the low frequencies but has a glitch in there - perhaps your cable or plug came loose?
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iphonetolaptop.jpg
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samsungtolaptop.jpg
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Re: Mirror Camera project

Postby Harry Dalek » Sun Jul 06, 2014 5:05 pm

gary wrote:Harry both of your files are still 44.1kHz stereo - so you are doing something wrong when recording.

Here are the response graphs - as you can see the samsung appears to be far superior in the low frequencies but has a glitch in there - perhaps your cable or plug came loose?


I tried it again here using Audacity but i think it is in stereo ...just down loaded it to try .

So its worth sticking with the Samsung for the tests .

i am not sure about the cable mmm i didn't notice a problem.

I was mainly looking for how well it did on the higher end i watched them my frequency scope screen as i recorded.

I set Audacity to 48khz with sound editor i set the recorder to 48khz and saved it to 48khz so i am not sure there ,i will stick with Audacity if its worked .
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Re: Mirror Camera project

Postby gary » Sun Jul 06, 2014 5:26 pm

That glitch at the start looks like a buffering problem in either the output player or the input recorder (see the gap in the audio below). Perhaps it is not worth worrying about as it only happens at the very beginning of the audio.

Yes the audio is still stereo see below for how to set it to mono.
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change to mono.jpg
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48ktest.jpg
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Re: Mirror Camera project

Postby Harry Dalek » Sun Jul 06, 2014 6:03 pm

gary wrote:That glitch at the start looks like a buffering problem in either the output player or the input recorder (see the gap in the audio below). Perhaps it is not worth worrying about as it only happens at the very beginning of the audio.

Yes the audio is still stereo see below for how to set it to mono.



Once again thanks for that work there Gary very helpful to know its doing one thing or the other .

So it was set ok at 48k much easier than the sound editor ,the glitch could be because these phones are touch screen perhaps time i took to press play and remove my finger .

I get ya on the mono setting now i was looking at the top tool bar ...another thing out of the way .

I was thinking of the next step of testing the sensor and head amp and or individually...more so the sensor the photo diodes and tranys just powered and have a resistor that might be cleaner than with the head amp circuit...solar cell test worked something i have not tried on the others .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Mirror Camera project

Postby gary » Sun Jul 06, 2014 6:41 pm

Sorry Harry, yes it was 48k. The 48k is more for your benefit than mine whereas the stereo thing is a pain as I have to keep removing the right channel each time I do an analysis - hence my selfishness ;-)
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