The Nth Monitor

Mast

17:35

@EBrown How many of those items are resistors, capacitors and other relatively cheap stuff?

EBrown

@Mast All but 1 lol

Mast

lol

EBrown

1000 1kohm resistors, 1000 4.7kohm resistors, and 1000 10kohm resistors.

@Mast What's the most general purpose capacitor size?

I need to find my amplifier drawings

Mast

@EBrown Either 100n or 47u, I think.

100n for normal caps, 47u for elco's.

EBrown

@Mast I actually found my old spice drawing that tells me what I need. :)

Mast

17:46

@EBrown Lacking those you can usually find helpful values in application notes as well.

Datasheets and application notes are your friend.

EBrown

@Mast Well this is for my own design item

Holy carp I need a huge resistor

357kOhm

Wtf for

Mast

You don't want a 357 Ohm resistor.

EBrown

Phew, that was about to be a lot worse than I thought

Mast

Not 357 kOhm either.

EBrown

Why not?

I can get a 360kOhm which is close enough

Mast

17:48

Pick a 360k instead.

@EBrown Because they're not part of the standard series, so more expensive.

It's all relative of-course, it's still only 7 cent a piece or something.

EBrown

Yeah I get them at 1c a piece.

Now I need to replace all the 19.1's with either 18 or 20...I wonder which one breaks my design more.

Mast

Simulate and find out.

Or, you know, get the division you currently have and find that same division using a different set with a look-up table.

But that would be, you know, way too professional.

EBrown

Gross

This is for a band-pass filter system

Hey @Mast do you know any way I can make my band-pass filter cutoffs sharper?

Mast

@EBrown Higher-order filter or a different kind of filter.

EBrown

@Mast Well I'm using capacitor-resistor.

With four low-pass and four high-pass filters alternating.

Mast

17:58

Should be quite good already.

EBrown

Yeah, it looks pretty sharp when I don't look at hotel whole DB scale.

LTSpice doesn't save my scale on each run.

The first filter is centered on 20hZ and seems to drop to -10dB by 250hZ or so.

That should be acceptable.

I just wonder if the overlaps are going to be a problem.

Mast

Overlaps?

EBrown

@Mast Yeah there are 15 filters here.

Mast

What exactly are you trying to do?

EBrown

@Mast Filter audio signal into 15 channels.

Mast

18:01

By frequency?

EBrown

Yeah

Mast

Wop.

EBrown

← 46 messages moved from The 2nd Monitor

Mast

Shouldn't you do that digitally instead?

EBrown

Filter it? I don't think so.

Mast

18:06

What's the endpoint of those channels?

EBrown

A slider to increase/decrease magnitude.

Mast

Like an audio equalizer?

EBrown

Yeah.

Mast

Hmmm.

I assume you're filtering each channel individually?

EBrown

Yep.

For the 20Hz channel I have 6.2kOhm resistor and 1uF capacitor.

Mast

18:10

In that case the overlap doesn't matter much, and the not-so-steep flanks are good side effects.

20Hz channel?

Channels should be bands of frequencies.

0-50, 50-100, things like that, not frequencies alone.

EBrown

Well it's centered on 20Hz.

Mast

Ok.

So, roughly 0-40?

EBrown

Yeah it's catching 10Hz to 25Hz pretty easily.

I think I'm off on the centre, I need to adjust it I think.

Mast

Do you know the type of filters you got?

EBrown

Yeah I designed them.

Crap just pushed that channel the wrong way lol

Mast

18:14

For audio you usually start with a Butterworth filter since they have a relatively good phase response and a relatively flat pass band.

EBrown

These are just basic low/high pass filters.

Mast

Oh, you went for first order filters.

EBrown

@Mast Yes.

Mast

Why don't you try a combination of coils and capacitors?

EBrown

I was younger then, lol

Didn't know as much as I do now, though I'm not sure how coils would help.

Mast

18:17

I'd definitely go for 2 third order filters instead.

EBrown

I then push each filter through it's own LTC6242 Op-Amp.

Mast

You can also go for the more often used C-L-C topology, saves you a coil.

Capacitors are usually cheaper.

But try and simulate the above.

EBrown

Drawing a new circuit out now.

@Mast Hmmm...

Seems to have a nice wave-form.

Mast

You can decrease or increase your Q factor based on how 'broad' a frequency you want to let pass.

EBrown

I need like a 3k inductor

Mast

18:28

lol

You won't find those.

3kH

EBrown

No kidding.

Mast

We can probably abuse the opamp somewhere in the filtering as well now I think about it.

Should even save you all inductors.

EBrown

I can't get this inductor to filter at a low enough frequency.

Mast

Oh, don't worry, there's a trick for that.

If only I could remember which one...

EBrown

Well I have it working at 10kHz.

Roughly.

Mast

18:34

Have you tried switching out all inductors for capacitors and vice versa? See what happens.

EBrown

For some reason it's amplifying my signal.

Mast

@EBrown That can't happen, it's a passive circuit.

EBrown

@Mast Signal comes in at -7dB, at 10.2kHz it's 3dB.

Mast

Without the opamp present yet?

EBrown

@Mast Correct.

Mast

18:37

Can't happen...

Passive components simply can't amplify.

They'd have to take the energy from somewhere.

EBrown

Right now the signal is being filtered up somehow...lol

@Mast ^^^

The blue trace is the V1 +, the green trace is the end of L2.

Mast

EBrown

What amp is that?

Mast

@EBrown Eh, that can't be right...

@EBrown A generic opamp, but this one should filter for you without needing inductor.

EBrown

Meh, I'll work on this later.

The RPi is more important.

I need $5.10 more in items for my cart for free shipping...

Mast

18:49

Put in a rail-to-rail opamp.

The 741 can't do rail-to-rail IIRC.

Or a ADC/DAC, or a power amplifier, or, think of something.

EBrown

I need another $1.10 in product to get free shipping...grrr...

Mast

A TAS2555 or something.

Audio amplifier controlled by I2C.

A TAS2552 if you prefer analog audio input.

Get a socket for them though, they're BGA.

Ball Grid Array

EBrown

Going to get some NPN and PNP transistors as well, is the TO-92 somewhat versatile?

Mast

Most common are the BC558 and BC548.

They are indeed versatile.

And usually available as TO-92, yes.

It's an old, common part. Often used in general schematics.

Heck, I'm building something at work at the moment that uses 2 of them.

Get the 5x9 version if you want a low-noise version, but the difference shouldn't be much.

Heck, have a wiki.

BC548

The BC548 is a general-purpose NPN bipolar junction transistor commonly used in European electronic equipment. It is notably often the first type of bipolar transistor hobbyists encounter, and is often featured in designs in hobby electronics magazines where a general-purpose transistor is required. The BC548 is low in cost and widely available. == History and usage == The BC548 is a part of a higher-quality family of NPN and PNP epitaxial silicon transistors that originated with the metal-cased BC108 family of transistors. This series, introduced in 1966 by Philips, became the most used ...

EBrown

@Mast Does it have a 2N number?

Mast

19:01

@EBrown Those are different. The BC548 is a transistor. The 2N4401 is an amplifier.

EBrown

Crap

That's why I am not finding what I want

Why would they list amplifiers in the transistors section?

Mast

Ah, well, there's the 2N3904, which is technically a transistor.

So many series, hard to remember what's in what.

There's the 4xxx, the 2Nxxxx, the 5xx, loads.

EBrown

These guys don't carry any useful transistors.

Mast

Sure? What site are you on, Mouser?

EBrown

No, All Electronics.

They're really cheap for resistors/capacitors.

I have 0.22uF, 0.1uF, and 47uF capacitors, are there any others I should get?

Mast

19:06

Depends, do you just want to build your specific schematic or do you want a lot of spares?

EBrown

Well I'm ordering bulk right now, so anything as general-purpose as possible.

I've ordered all my specific parts, now I just need to get to $75 for free shipping.

Mast

@EBrown Yuck, what a crazy site of electronics. No specs.

EBrown

@Mast Yeah I know. :(

Mast

I'd go for sets. You can usually get things like 10 resistors each on the entire E12 series for less than 10 bucks.

1 to 1M

You could get yourself the parts for a buck-boost converter, always fun to build those.

EBrown

Buck-boost converter?

Mast

19:11

A switched mode power supply that can both boost (higher output voltage than input) and buck (lower output than input). DC-DC.

EBrown

Nifty

Mast

Had to build one back when I was in college.

EBrown

Ordering my $88 in parts.

Mast

You usually pick something of an oscillator and hook it on a mosfet for the switching, the rest is just passive components.

But they're dirt cheap as pre-built as well.

EBrown

19:47

@Mast Just found my ECG Semiconductor Master Replacement Guide (ECG212P).

Mast

20:15

@EBrown I've heard about it, don't have one myself though.

Duga

23:45

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