Op Amps... Boost my output

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Op Amps... Boost my output

Postby FlyMario » Wed Jun 01, 2022 3:40 am

So, I realize this is in the mechanical TV forum but the circuit I am trying to build is for a mechanical tv... does that count?

I am using a dfplayer mini to put out the mutr15.wav video signal. It seems to be doing fine however the output appears to be from 0 to about .8v-or ..9v dc. The signal is also upside down and I am assured this is fine and not abnormal.

The thing is though, I keep thinking I want the output to be 0 - 5vdc. It feels like it would be easier to pick out the synch pulses at that point.

I have a bunch of LM358 and some ca3140 op amps. Is there a simple way that a circuit could be designed that would boost that < 1v to a peak of 5v? I see a lot of OPAMP circuits online but I am not that great of an Analog person.

Any ideas?

thanks!
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Re: Op Amps... Boost my output

Postby Steve Anderson » Wed Jun 01, 2022 12:34 pm

That's all quite easy to do, but first a few questions:-

1) What power supply voltage(s) are available?
2) What will this stage/amplifier be driving? i.e. What's the load?
3) Frequency response? Simple audio, 20Hz-20kHz, or more/less?
4) Does this need to be DC-coupled?
5) Maximum and minimum gain? It seems about 6 plus/minus a reasonable amount, say 4 to 10?
6) Any preferred parts, those you already have?...Just noticed, you have some LM358 and some ca3140 op amps.
7) Inverting/non-inverting? Or switchable (both)? Generally a good idea in NBTV to provide both.

Any 'special requirements' outside of the above?

That may seem a lot, but any circuit designer is probably going to ask the same...

I'm assuming the source will be the module you mention...

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Re: Op Amps... Boost my output

Postby FlyMario » Thu Jun 02, 2022 12:39 am

Ok, so some of these are confusing for me.

1) the supply voltages are 5v and 12v. Both are DC Regulated. The 5v is what I planned to drive the circuits and the 12v to run the motor. The 5vdc will come from an lm7805 connected to the 12v supply.

2) I am not sure what you mean. The output will go into another LM358 used as a comparator to look for the synch signal.

3) 20khz seems good. I am reluctant because the .wav file is 41.1 kHz ... I can't see how I need to sample it more than 20khz. (who comes up with these odd bitrates anyways?)

4) Not sure if that is necessary. the output signals seem to be strictly DC. if you think that is a good idea then yes.

5) The gain should be about 1v in and the output should be around 5v. I imagine you lose some. But I think that should be fine.

6) LM258. I do have CA3140 if that is a better device.

7) switchable.

The input would be from A DFPLAYER Mini. As I said, it seems the output from the DAC at slightly under 1vdc.

Thanks!
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Re: Op Amps... Boost my output

Postby Steve Anderson » Thu Jun 02, 2022 11:49 am

FlyMario wrote:Ok, so some of these are confusing for me. The input would be from A DFPLAYER Mini. As I said, it seems the output from the DAC at slightly under 1vdc.

Thanks!


OK, no problem, we'll sort it out one way or another. My answers are in this colour...

1) the supply voltages are 5v and 12v. Both are DC Regulated. The 5v is what I planned to drive the circuits and the 12v to run the motor. The 5vdc will come from an lm7805 connected to the 12v supply. With a 5V supply both those op-amps are not going to be able to give you a 5V p/p output, maybe 2V, 3V at best. Far better to use the 12V supply suitably filtered to hopefully eliminate the noise injected from the DC motor (presumably brushed).

2) I am not sure what you mean. The output will go into another LM358 used as a comparator to look for the synch signal. That should be OK, I'll know when I see the circuit(s).

3) 20khz seems good. I am reluctant because the .wav file is 41.1 kHz ... I can't see how I need to sample it more than 20khz. (who comes up with these odd bitrates anyways?) More below...

4) Not sure if that is necessary. the output signals seem to be strictly DC. if you think that is a good idea then yes. The DFplayer appears to be AC-coupled itself, so that question goes away...

5) The gain should be about 1v in and the output should be around 5v. I imagine you lose some. But I think that should be fine. Agreed.

6) LM258. I do have CA3140 if that is a better device. See below.

7) switchable. Noted.

I'll append the other part in a while....things to do right now...

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Re: Op Amps... Boost my output

Postby Steve Anderson » Thu Jun 02, 2022 12:13 pm

Let's start at the beginning...what power supply are you planning to use for this? A ready-made one or one you'll make up yourself?

I'll go through this step-by-step as what you decide here affects later decisions...many, if not all, are interrelated...

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Re: Op Amps... Boost my output

Postby Steve Anderson » Thu Jun 02, 2022 2:02 pm

Item 3), Yes, why 44.1kHz when most other audio sampling rates are an integer multiple of 1000Hz? There is a good reason for this, it stems from the two different line rates of 15,625Hz (EU) and 15.750kHz (US) used for most analogue TV. Klaas Robers did explain exactly the maths behind this a few years ago. It seemed sensible, but I cannot recall now how was derived. As the CD has gone the way of Beta, VHS and others (dead) it really doesn't matter anymore. 22,050Hz and 11,025Hz are simply sub-multiples of it. Even the sampling rate of the telephone system at 64,000 bits/sec comes out to a nice round 8,000 bytes/sec (8kHz) - a theoretical audio bandwidth of 4kHz - good enough for telephony.

The other items really shouldn't need any further expansion, but I will if you're still quizzical or confused.

Steve A.

Here's a good explanation of audio, compression, sampling rates and bit-depth from the BBC...video too...(just think of NBTV video as audio - it's just a special type of audio)....

https://www.bbc.co.uk/bitesize/guides/z ... revision/1

Factoid:- The sampling rate of DVD audio is 48kHz, not 44.1kHz. Recording studios often use 96kHz or 192kHz sampling at 24 bits for mastering, when the mix-down is complete it is bit-reduced and sample-rate reduced to 48 or 44.1kHz at 16 bits as required.
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Re: Op Amps... Boost my output

Postby Steve Anderson » Thu Jun 02, 2022 3:03 pm

I've found some notes r.e. 44.1kHz...

Why 44.1kHz?

60Hz Video...

245 Active Video lines used per field, 3 16-bit samples per line per channel

60x245x3=44100 samples/sec/channel

50Hz Video...

294 Active Video lines used per field, 3 16-bit samples per line per channel

50x294x3=44100 samples/sec/channel

Both line rates are quite close, @ 50Hz-15.625kHz...@ 60Hz=15.750kHz (+0.8%)


....I knew I had it somewhere...

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Boost my output

Postby acl » Thu Jun 02, 2022 9:01 pm

Capture.JPG
Try this one
Capture.JPG (76.47 KiB) Viewed 6209 times
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Re: Op Amps... Boost my output

Postby FlyMario » Thu Jun 02, 2022 9:26 pm

Wow thanks a lot!

We can use 12v then. No Problem. I am using a bench power supply now but I plan on using a 12v regulated power supply. The typical metal ones where you have screw terminals. I think I will need around 2 amps as the motor takes around 1amp if I stall it.

I am using a brushed motor. It is geared internally at around 1000 rpm @12v

I kept saying LM258... geez. It is LM358. I have probably 100 of them from each time I started to make a Mechanical TV.

Funny what you said about 44.1khz and the rest. We all seem to be very stuck at 60 and 50 hz.

Also, good news is that I have ordered a 15" disk from the club. In the meantime I am using a disk I designed in Solidworks and printed.

Thanks a lot!
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Re: Op Amps... Boost my output

Postby FlyMario » Thu Jun 02, 2022 11:15 pm

I think I figured it out... ACL must be Chris. I got an email with the club handbook.

This handbook is really really nice.

Going out of town this weekend. Going to print it out.

Seems it has a lot of circuits that use my familiar components as well. Not that I know how to use them that much. Mosfets and arduino's are my normal.

Have any of you gotten the CD4046 PLL circuit to work properly? The circuit in the book looks so nice and I feel that it must be pretty reliable. One time I worked with a 4046 and the signals coming out were not very digital. It had a triangle waveform that shifted left and right depending on if it is out of sync.

Thanks!




Thanks!
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Re: Op Amps... Boost my output

Postby acl » Fri Jun 03, 2022 2:12 am

Hi there Peter,

The output signal from the 4046 is tri-state that is to say logic one to drive the motor speed up open circuit to let the motor speed coast down and zero to really slow the motor down.

Hope this helps
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Re: Op Amps... Boost my output

Postby Steve Anderson » Fri Jun 03, 2022 11:15 am

FlyMario wrote:I kept saying LM258... geez. It is LM358.


There is/was such a beast as the LM258 (and even a LM158). They are basically all the same, except their temperature ratings.

LM358 Ambient temperature 0 to +70 celcius, (Commercial).

LM258 Ambient temperature -25 to +85 celcius. (Industrial).

LM158 Ambient temperature -40 tp +125 celcius. (Military/Aerospace).

There is also a rating called 'Automotive', somewhere between Industrial and Military/Aerospace. The temperature limits vary slightly between manufacturers. Each manufacturer has a different way of marking the devices to indicate its temperature rating. It's always (somewhere) on the datasheet. It's on page 2 of the attached National LM158/258/358 datasheet...

You'll notice that there's a lot of data and graphs that relate to temperature on all datasheets. As most devices are Silicon-based they are by definition temperature sensitive. To a large degree (pun not intended), that can be designed out. But sometimes it can be useful, e.g. temperature sensors...

Likewise with light. The vast majority of Silicon devices are in metal cans or I.R. and visible light opaque black plastic. Exceptions are photodiodes, phototransistors and the like. They can be in a clear casing or I.R transmissive black plastic that blocks visible light but passes I.R. TV remote control receivers for example.

Steve A.

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