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1  Using Arduino / Project Guidance / Re: Display values using adjustable water level on: May 24, 2012, 10:02:42 am
I'll play with the balloon idea this evening, now that I have my new servos. (The old ones I burnt out in other experiments smiley)

The level will be more than accurate enough just using software-based calibration I think, no need for anything so precise as pressure sensors. I'm not sure how much I'd need to spend to be able to detect the difference in pressure of a column of water only 4mm across over 5cm (at max!) of movement! Someone opening the room's door would probably have more impact.
2  Using Arduino / Project Guidance / Re: Display values using adjustable water level on: May 24, 2012, 09:27:51 am
I think a pump will be way over-kill, the amount of water is only going to be enough to fill some little tubes smiley

Great idea with the balloon-twisting though Techylah!

I found some tubes virtually free on eBay, that have a mere 4mm internal diameter. That means for even a 5cm maximum-deflection, I'll only need to move less than 1ml of fluid. I'm hoping that the perspex tubes will still show the level enough. Throw in a bit of coloured light and they should look pretty enough.  Experimentation is key here, I think smiley-wink

3  Using Arduino / Project Guidance / Re: Display values using adjustable water level on: May 22, 2012, 07:46:56 am
Okay, I've ordered some larger syringes, as the only ones I had lying around were little 5ml ones. They would require both a thin "display" tube to make a decent difference in level, and also a long "draw" to move the level up and down.

I've ordered some 50ml and 100ml syringes, and I'm hoping that if I have a small-ish (5-10mm) display tube, then the fatter syringes will need much less movement to affect the water-level as required. That way I can cut the syringes as short as I need.

The problem then will be how to connect a servo to the plunger in a useful way. I've seen some linear servos, but they are a little pricey for testing, and eventually I'll need 8 of these. Can anyone suggest a simple alternative? Currently I was thinking of a simple lever attached to a servo-horn. Which reminds me, I need to buy some more servos smiley

Basic requirements would seem to be:

  • 20-40mm travel distance
  • powerful enough to push/pull a syringe plunger
  • accuracy not critical, as long as I can get maybe 10 positions from "lowest" to "highest"
4  Using Arduino / Project Guidance / Re: Display values using adjustable water level on: May 17, 2012, 07:51:46 am
Thanks, that's what I was thinking so far. I probably just need some sort of servo strong enough to pull/push the plungers (which can be very stiff), or perhaps use a threaded rod/motor combo of some sort.  I probably need to draw some more ideas, maybe prototype some stuff together. I'm really good at the whole "coming up with ideas but never getting anywhere with them" thing, so need to change things around a bit smiley
5  Using Arduino / Project Guidance / Display values using adjustable water level on: May 16, 2012, 06:15:30 pm
Here's an odd idea I'm toying with, but I can't quite work out a decent practical way of implementing it.

I want to have a device which will form a kind of gauge, with the value being represented by the fluid-level in a small cylinder. I'm thinking in the range of ~2cm diameter for the tubes.



What I really need is some inspiration for some mechanism that will raise and lower the level to particular points, whilst not becoming to large.

Here are some initial thoughts (bearing in mind there will need to be several of these in the display):

  • A syringe with the plunger fixed to some sort of linear actuator
  • Some sort of compressible bladder
  • A reservoir behind each tube, into which a mass can be lowered to raise the fluid-level
  • A cheap and/or home-brew peristaltic pump
  • A future-tech nanofluid that expands directly proportionally to a voltage applied through it*

Any comments? I'm hoping I've missed something obvious smiley

(*ideally non-sentient)
6  Using Arduino / Motors, Mechanics, and Power / Re: Driving a PC fan - transistor with or without an optocoupler? on: March 24, 2012, 03:32:32 am
Yeah, the diode there is a silly mistake. I only used a 317  because that's what I had lying around.
7  Using Arduino / General Electronics / Re: Soldering Irons on: February 25, 2012, 10:46:34 am
Wow, great info. Thanks smiley
8  Using Arduino / Motors, Mechanics, and Power / Re: Help identifying a computer PSU - non-standard HP molex? on: February 15, 2012, 05:46:14 pm
Yeah, I'm keeping green grounded. A tiny bit of load keeps it going okay.
9  Using Arduino / Motors, Mechanics, and Power / Re: Help identifying a computer PSU - non-standard HP molex? on: February 15, 2012, 05:19:38 pm
That's what he did.  The PSU needs a load to continue running.  A lot of PSUs don't work without a load.

oh no it isn't
Yes it is. So exactly what I said in my original post then
10  Using Arduino / Motors, Mechanics, and Power / Re: Help identifying a computer PSU - non-standard HP molex? on: February 15, 2012, 11:13:08 am
They are pretty old smiley  The fact it's plastered in "HP Compaq" is a bit of a sign.  It's quite a neat form-factor though, so I thought I'd use it.  Now to get rid of the elevendyone wires coming out of it...
11  Using Arduino / General Electronics / Re: Smothing a PWM signal for use with a PC fan on: February 12, 2012, 01:55:25 pm
I'm not quite sure what you mean by "before the power output stage".  Do you mean boost the PWM signal coming out of the Arduino to 12V, and then smooth it?

Incidentally, cranking the PWM frequency to 31kHz solves the buzzing of the fans, but not the tacho, so I think I'll still need to investigate this emitter-follower, boosted signal setup smiley
12  Using Arduino / Motors, Mechanics, and Power / Re: Help identifying a computer PSU - non-standard HP molex? on: February 12, 2012, 01:29:39 pm
Oh, I tried with a little resistor/LED pair and it worked!  The fans must be too small a load perhaps.
13  Using Arduino / Motors, Mechanics, and Power / Re: Help identifying a computer PSU - non-standard HP molex? on: February 12, 2012, 01:26:03 pm
Hmm, maybe I need more load?  I tried two fans, but they just spin for <1sec then stop.
14  Using Arduino / Motors, Mechanics, and Power / Help identifying a computer PSU - non-standard HP molex? on: February 12, 2012, 01:01:41 pm
Hello,

I was thinking of re-purposing an old HP/Compaq desktop PSU for use on a project that needs 12V, but I'm having trouble getting the PSU to start up.  I've used ATX supplies before, and have therefore had to short the POWER_ON connection to get them to start, but this unit seems different.

For starters, instead of a 20- or 24-pin Molex, this one has a 10-pin and an 8-pin Molex.

So connector one looks straight forward enough - a bunch of grounds, a pair of 5v red and a pair of 12v yellow:
Code:
    red black black yellow
    red black black yellow

Connector two looks like the cleverer one:
Code:
    blue   yellow purple green black
    orange   n/c    n/c   n/c  black

Now, if I power the thing up connected to a motherboard, I get pretty much what I expect from the ATX documentation I've seen, which is:
Blue: -12V
Orange: +3.3V
Yellow: +12v
Purple: +5v (STANDBY - this is always on)
Green: 0.06v (POWER_ON)

However, disconnected from the motherboard, when I manually short POWER_ON to GND, I get a blip of power, but it drops straight back down to zero.



The PSU has the following label:

COMPAQ COMPUTER CORPORATION
Model: HP-L1520F3P
Part Number: 308446-001
Spare Number: 308619-001

It's apparently a "308446-001 HP Compaq power supply 150 Watt for Evo D530UST ultra slim desktop PC" and this is what it looks like.
15  Using Arduino / General Electronics / Re: Smothing a PWM signal for use with a PC fan on: February 12, 2012, 04:18:49 am
Great, thanks. Now I can move on to the smoothing issue. I imagine that'll result another question or two  smiley
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