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Messages - jbeale

121
General discussion / comparing Sparkfun and Pololu 5V boost circuits
I recently compared two similar 3V -> 5V boost circuits, the Sparkfun  #08999 5V out @ 100 mA (based on NCP1400) and the Pololu #798 5V out @ 200 mA (based on NCP1402).
http://http://www.sparkfun.com/products/8999
http://http://www.pololu.com/catalog/product/798

The details are below, but the executive summary is: the Pololu 5V boost circuit module has 2x max current and it is cheaper, smaller, has lower noise, and is more efficient at every load current, as compared with the Sparkfun module.

(note: I regularly buy from both Sparkfun and Pololu, but have no other relationship to either company.)

Sparkfun #8999 NCP1400 5V out 100 mA circuit. Measured at 3.2V input, resistive load:
Efficiency vs current out: 81% @ 25 mA, 67% @ 50 mA.
Noise on 5V, 50 mA out: 34mVrms, 300 mVpp (20 MHz BW) 40 mVrms, 600 mVpp (100 MHz BW).
With 5 V, 25 mA out: 18mVrms, 230 mVpp (20 MHz BW), 28 mVrms, 400 mVpp (100 MHz BW).
Current draw from 3.3V with no load: 1.2 mA

Pololu #798 NCP1402, 5V out, up to 200 mA with >2.7V in. Measured at 3.2V input, resistive load:
Efficiency vs. current out: 81% @4 mA, 84% @25 mA, 86% @50 mA.
Noise on 5V out: 10 mVrms, 50 mVpp in 20 MHz BW and 14 mVrms, 100 mVpp in 100 MHz BW
(independent of load current, over tested load range)
Ripple frequency variable, increases with load current:
5 kHz @ 4ma, 50 kHz @ 50 mA output. Vout: 5.004 V to 5.010 V (Vout increases with higher load).
(2nd unit tested, Vout= 4.98 V.)
Current draw from 3.3V with no load: 200 uA

122
General discussion / Re: cheap adequate 18V 3A bench supply?
Thanks Arhi for the very informative and detailed reply! I somehow had the impression that the PC switching supplies would become excessively (electrically) noisy under very light or no load, but maybe that is no longer true with modern designs (?)  Even my digital stuff usually has some analog component to it, like measuring time intervals to high precision, where supply rail noise that can shift the logic threshold slightly can make a difference.  Hmm... I actually have an unused ATX supply under my bench right now, so I guess I should actually measure it and see.
123
General discussion / Re: cheap adequate 18V 3A bench supply?
Thanks brian- I'm doing the typical small, low-power analog and digital circuits, and usually don't need more than 1 A.  Checking Ebay, I see a used HP 6213A for about $65, although I also see gq_electronics_llc has a new 15V 2A "GQ-1502" supply w/digital displays, reasonable specs, for $58 but I'm wondering if it is more noisy, or likely to break.
124
General discussion / cheap adequate 18V 3A bench supply?
I know there is a project here to build a superior lab bench power supply / multimeter / etc tool, but in case I just want a fairly cheap, utility bench power supply, available now off the shelf, can anyone comment if this one is likely ok (given the $80 price)?

MASTECH HY1803D 18V, 3A, adjustable V/I, LCD meters for V and I.  ($80 at Amazon)
http://www.amazon.com/MASTECH-HY1803D-V ... roduct_top

The reviews in Amazon are overall ok. I just wanted to check if anyone here had experience with this particular model, and can comment if there's any reason not to buy it.  I googled this supply, and mostly found comments from people who seem to be unfamiliar with power supplies in general.

I notice Sparkfun sells a very similar-looking unit (Extech 382202), also 18V, 3A for almost twice the price, and its LCD voltmeter only resolves 100 mV (vs 10 mV on Mastech). SF reviews for it seem ok (except RFI resets caused by powering 2M ham transmitter).  http://www.sparkfun.com/products/9293
125
General discussion / Re: anyone used very fine "NYLACLAD" wire ?
It is a good suggestion. I see that I have some #44 strands here that are a lot easier to work with, and for this application I can make do without the insulation. I'd still like to know how anyone uses the insulated ultra-fine wire-  maybe some other day.
126
General discussion / anyone used very fine "NYLACLAD" wire ?
I want to mount a small 4-pad SMT part in a tight spot where it is awkward to put a PCB of any size. So, I figured I'd just solder some fine wires to the pads on the back. The 30 gauge wire-wrap type wire I have is a bit too big- it is stiff enough that flexing the wire would probably break it off the tiny pad.

That leaves a spool of VERY fine wire I got at an electronics surplus store. Thinner than a typical hair, it looks and feels like a strand of spiderweb. The spool is unmarked except it reads "Hudson Wire Company" and "NYLACLAD".  It is insulated copper and I wonder if the insulation is nylon (?)  I measured the wire resistance to be about 35 ohms per meter, from an online calculator that indicates this is 50 gauge wire (Cu core is 0.025 mm diameter).  My calipers say 0.03 mm but they only resolve 0.01 mm, and anyway that's including the insulation.

My question: has anyone worked with this type of insulated wire? What is the best way to strip it? The insulation seems pretty tough because I can work the wire back and forth in a blob of molten solder and it only sometimes seems to form an electrical joint.  Pulling too hard on it, of course, causes a break.  I've sanded off the enamel insulation on some magnet wire, but this stuff is too fragile for that.
129
General discussion / TI TMP006 infrared sensor does seem to work
I got the eval kit for the TI TMP006 sensor mentioned here last week. It does seem to be able to detect the presence of my hand (apparently about 37 C), when I place it in front of the sensor and then remove it (so the sensor sees just the surface of my desk, around 25 C).  The sensor sits in the open on a flat PCB. I wonder if it would be a bit less noisy if it was semi-enclosed and shielded from stray air currents.

[attachment=0]

NOTE: putting the sensor in a plastic bag much reduced the noise, and it still works otherwise same as before. The local chip temperature does rise more above ambient due to self-heating.
131
General discussion / Re: Microchip Arduino thing interview questions?
I'm interested in using the PIC32's timer input capture mode to measure pulsewidths with better accuracy (80 MHz clock = 12.5 ns resolution) than I can get with a stock 16 MHz Arduino.

Are there any examples of such a thing online?  Can it be done using the Chipkit version of the standard Arduino dev environment? Which timers does the system use (eg. millis() clock)?
132
General discussion / Re: testing Digilent chipKIT Uno32 board
Ok, using   
Code: [Select]
   PORTG = B00000000;  // PortG pins low
   PORTG = B01000000;  // PortG.6 = Arduino Digital Pin 13 high
   PORTG = B00000000;  // PortG pins low
   PORTG = B01000000;  // PortG.6 = Arduino Digital Pin 13 high
I see that the Uno32 can generate a 40 MHz square wave output (12.5 ns per instruction), but only after the first transition which takes twice the time (25 ns), I guess some kind of pipeline effect (?)
133
General discussion / testing Digilent chipKIT Uno32 board
My Uno32 just came in the mail. I've confirmed that the delay between digitalWrite() instructions is about 5x faster than Arduino, based on the below sketch. However, I'd like to try direct assembly- is that possible using the modified Arduino-chipkit dev environment; if so how? ...or do I have to go to a different dev environment?  I'll also check over at http://www.chipkit.org/forum

Code: [Select]
void loop() {
  digitalWrite(13, HIGH);   // set the LED on
  digitalWrite(13, LOW);    // set the LED off
  digitalWrite(13, HIGH);   // set the LED on
  digitalWrite(13, LOW);    // set the LED off
  delay(1000);
}

// viewing waveforms on scope:
// Arduino: 3.82 usec between "high" & "low"
// Uno32: 740 nsec between "high" & "low"  about 5x faster
134
General discussion / Re: ARGHH! USB wiring pinout - I've created a monster?
In fact, the version on my web page since November says essentially that. But from Google, it looks like no one has copied that one! I think people copy the first one they see in the image search, which is no longer the one on my page. It's just one of those ways in which the web does not work optimally.
135
General discussion / ARGHH! USB wiring pinout - I've created a monster?
It started as a simple mistake. Back in 2007 I made an illustration of the USB wiring pinout for a quick writeup explaining an external battery pack for powering a USB device on my webpage: http://www.bealecorner.org/best/measure/USB/index.html

Except that on the original image, I mislabeled it: the USB DATA+ and DATA- wires were reversed. I did not realize it then, since I was only using the +5V and Ground wires.  I fixed my own web page about 6 months ago (DATA+ should be GREEN), but it had been up for some time and the damage is done... the old (incorrect) image got copied all over the web (see Google image search below) and when you google for images of "USB wiring", the very first hit is my old, wrong image, on some .ie domain webpage that has no contact info.  I'm guessing there's no way to fix this now...

http://www.google.com/search?q=USB+wiri ... 01&bih=940

There are even two separate versions of this photo with labels translated into Spanish, both still with the wrong pinout.

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