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Offline joe61Topic starter

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Help with a schematic
« on: May 04, 2011, 04:21:14 PM »
My wife likes to sleep with the sound of a motor of some kind running, like a fan or air conditioner etc. Just a steady hum. So I'm trying to make use of some small motors I've got in a drawer and setup a noise maker for her. The motor will have a piece of paper or cardboard attached to it, which will hit the case and make a humming sound.

I'm setting a timer in the code, and after an hour it will spin down the motor slowly and put the chip to sleep.

I'd appreciate comments about the schematic and board layout. Since this will be plugged into the wall and be left all night. I'm particularly interested in the fuse, I've ordered some PTC fuses with a trip point of 600mA. Since there won't be any load to speak of on the motor I'm thinking that will be ok. Am I missing something there?

Appreciate any comments.

Thanks

Joe

Offline Soeren

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Re: Help with a schematic
« Reply #1 on: May 04, 2011, 06:43:59 PM »
Hi,

My wife likes to sleep with the sound of a motor of some kind running, like a fan or air conditioner etc. Just a steady hum.
Tinnitus?
Whether or not, I'd suggest making a rain/wave sound simulator instead, as this will be more controllable, use less power and will be adjustable in several ways - sound level, "bandwidth" and "center frequency" (white, brown, pink, grey, blue or purple noise and variations hereof, if that makes any sense to you), sound envelope (ADSR) and repetition period.
This way it can be made to sound like anything from a light rain to a thunderstorm, from light waves to a bit less than a tsunami.

This is a known help for tinnitus and as a general mind soothing relaxation aid and I'm sure it will help your other half to sweet dreams :)
Small mods could make it sound like what u want to make mechanically - still with far more adjustable - like eg. a long slow fade out without changing the sound - try that with a motor ;D

And less mechanical means longer life (for the parts, sadly it doesn't have the same effect on the user).


I'd appreciate comments about the schematic and board layout.
Well, you're asking for it  :P  ;D


[...] Since there won't be any load to speak of on the motor I'm thinking that will be ok. Am I missing something there?
The Schematic:
Fusing
Always use separate fuses for each branch (i.e. one for the line going to the motor and one for the line to the regulator).
Transistor
The emitter of Q1 should go to 0V and the motor goes between +12V and the collector. As it stand, the controller won't be able to open Q1 and might damage the controller through leakage from collector to base. The base of a TIP120 must be around 2.5V positive with reference to its emitter for it to open.
Regulator
I'll recommend around 220nF from input to ground, as close to the terminals/pins as physical possible.

As I'm not sure about the purpose of JP1, I can't tell you if it's good or bad, but I'm sure you have a purpose for it  :)

The Board:
Traces
Nobody would rapelle down a mountain side with sewing tread and that's for the same reason that you shouldn't use hair line traces on a PCB.
More than half of the trace voltage drop caused by the motor will enter the controller - route all power lines starting where the line enters the board.
Avoid sharp corners if possible (and they all avdablare on your PCB).
You have an acid trap on the top layer on the middle pin of JP1
Seems like you're shorting your power input.
No reason to use double sided PCB, single sided is cheaper and easier.

Well,let's leave it at that, no reason to get you depressed ;D


Even if you tidy up both schematic and PCB and gold-plate the latter, I'd still prefer the aforementioned sound generator - If interested, I can dig up the schematic and board for a pretty simple unit that can be modded fairly easy.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline joe61Topic starter

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Re: Help with a schematic
« Reply #2 on: May 04, 2011, 07:21:20 PM »
Tinnitus?
Whether or not, I'd suggest making a rain/wave sound simulator instead, as this will be more controllable, use less power and will be adjustable in several ways - sound level, "bandwidth" and "center frequency" (white, brown, pink, grey, blue or purple noise and variations hereof, if that makes any sense to you), sound envelope (ADSR) and repetition period.

I don't understand what you have in mind for the sound generator, but it sounds interesting. How would you do that?

Quote
The Schematic:
Fusing
Always use separate fuses for each branch (i.e. one for the line going to the motor and one for the line to the regulator).

Ok, that makes sense. Was the trip value of the fuse I ordered ok? I'm not sure I understand the different values in the data sheet.

Quote
Transistor
The emitter of Q1 should go to 0V and the motor goes between +12V and the collector. As it stand, the controller won't be able to open Q1 and might damage the controller through leakage from collector to base. The base of a TIP120 must be around 2.5V positive with reference to its emitter for it to open.

That's odd, I built  a prototype that works as expected. PWM control of the transistor, etc.

I just looked again and realized that I forgot to change the unregulated supply symbol. It's not really 12 volts, more like 6. Sorry.

Quote
As I'm not sure about the purpose of JP1, I can't tell you if it's good or bad, but I'm sure you have a purpose for it  :)

It's a connection for a potentiometer so she can change the speed of the motor.

Quote
Even if you tidy up both schematic and PCB and gold-plate the latter, I'd still prefer the aforementioned sound generator - If interested, I can dig up the schematic and board for a pretty simple unit that can be modded fairly easy.


Glad I posted that here before sending it off, sounds like I would have wasted some money.

Thanks

Joe

Offline Soeren

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Re: Help with a schematic
« Reply #3 on: May 04, 2011, 08:20:24 PM »
Hi,

I don't understand what you have in mind for the sound generator, but it sounds interesting. How would you do that?
I just tried uploading a PDF of the unit, but for some reason it kept breaking the file (wonder if it's because I have more than 4 times the amount allowed).
I'll try again tomorrow.

It's an analog unit and while it can be made in a controller, I believe it sounds better with analog processing, unless you're a skilled DSP champ with a fast controller.

In essence, you do it much like how the speech is generated from received codes in a cell phone.
You start with white noise, add different filters, envelope control etc.
For a rain sound, a couple of filters may do, as the ADSR is just to modify the filters dynamically, to simulate the sound of waves breaking.


Was the trip value of the fuse I ordered ok? I'm not sure I understand the different values in the data sheet.
I can't say.
For the regulator, you probably need the lowest value available, as it takes next to nothing (compared to fuse ratings).
For the motor, you need it to sustain a peak close to stall current at startup, so in terms of regular fuses, use a value in between the normal running current and the stall current and get a "T" (slow-blow) or a "TT" (even "slower") fuse.


That's odd, I built  a prototype that works as expected. PWM control of the transistor, etc.

I just looked again and realized that I forgot to change the unregulated supply symbol. It's not really 12 volts, more like 6. Sorry.
That explains why the controller didn't take a hit at least.
Try measuring the voltage drop (collector emitter) as it is, and how it should be.
The base has to be around 2.5V higher than the emitter, so if you put 5V on the base, the emitter will be at around 2.5V, so not much juice for the motor.
If you move it to the low side of the motor instead, you won't have that problem.


It's a connection for a potentiometer so she can change the speed of the motor.
OK.


Glad I posted that here before sending it off, sounds like I would have wasted some money.
If that was your final board layout, yes... But at least the people at the PCB facility would have been amused  ;D
A board that simple could be made on your kitchen table, or you could use strip-board.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline MikeK

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Re: Help with a schematic
« Reply #4 on: May 05, 2011, 04:05:13 PM »
Just wondering...Doesn't relying on a noise machine make the situation worse by creating a crutch?  I've had insomnia for over 6 years and went through a big mess with different things.  Learning to meditate is helpful.

Offline Soeren

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Re: Help with a schematic
« Reply #5 on: May 08, 2011, 05:10:22 PM »
Hi,

Tried numerous times over the last days to upload the file, but fo some reason it keeps breaking, even a minute ago where I got to get the full file up, a test download revealed that it was bad (although the exact size - must be the signature of the file triggering something on the server) :(
So, I tried to upload just the schematic and no problem - if you need a board layout, it will probably upload as a separate file, but I'll only do it if you need it, as I'm more than 4 times over the allowed storage on the server.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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