Modifying YDS-812 buck converters

These buck converters are great; readily available on Ebay for about $4 a pop.


Wins:

• Well heatsinked, well made
• Synchronous  for higher efficiency
• Easily modified in useful ways

Official datasheet is here - however practical experience actually you can ignore quite a lot of it :-)

The over-current shutdown doesn't seem to work very well (I pulled 13A @ 5v out of one) and the minimum voltage spec is also pessimistic - when modded you can run them on lower voltage inputs. YMMV of course.

The main control chip is the Texas Instruments LM2727

The fets are 52N06 fets

Firstly; you MUST add electrolytic capacitors on the input and outputs or they just don't work; I put e.g. 1000uf (e.g. 35v) on the input and 2500uf on the output. You should use low-ESR caps.

Adjusting output voltage

On the PCB, VR1 is 1k,  VR2 is composed of an 18k (on the left) and a 1k (right) in series = 19k.

The controller wants to see 0.6v on the FB input, so the default divider values of 1k & 19k gives you 

12v 'input' (buck output) = 0.6v output (feedback to chip). 

The resistor divider calc is of course (19k+1k)/1k * 0.6v =12v at Vout  

When modding this board for lower voltage output I find it easiest to piggyback an extra 0402 resistor on top of the 18k one 

Here's the datasheet sample schematic that roughly matches what we have on the board (minus the 5v regulator, FET driver and other bits and pieces)...

Soft on/off

The transistor just above VR1 on the board is an internal on/off switch (not sure when it's used), but if you solder a wire onto the right hand side pin of it (according to the above pic) you get access to /SD; pull this low and the buck switches off.  Note it has an extremely weak (microamps) 5v pullup on-chip.

How to fix Crucial V4 SSD I/O errors

I use a 32GB Crucial V4 SSD for the OS drive of my home theater PC; it's not a great drive but it works.. well, up until today, when an unexpected powerdown corrupted it. I tried to reimage the drive (I use "DD" under linux) but I got a bunch of IO errors writing to the SSD. DOH!  Normally I'd bin the drive and buy another one (hint; not a Crucial drive) but this time I found a fix...

If you re-flash the drive's firmware (using the bootable usb stick image found here ) it cautions in the docs here "!ALL DATA WILL BE LOST!"   ...well, y'know actually that sounds ideal...

And lo! Even though my drive was already running the latest firmware, the tool allows you to reflash it anyway, and bingo - twenty seconds later a completely blank SSD with no hard errors.

Happy new year!

Powering a lot of WS2812B LEDs from a 12V car battery - try this!

Ok so let's say you need to power a shit-load of WS2812B LED strips from e.g. a car battery.
You need to convert ~12v to 5v and you need a lot of current.
You also want high efficiency, and you'd like to be able to power them down completely to avoid the ~1ma-per-led quiescent current..

While perusing buck converters, I came across this, and was immediately curious... It's about $10 a pop.

http://www.prodctodc.com/dc-1014v-to-255v-15a-buck-converter-peak-20a-high-current-power-supply-p-121.html
also on Ali-express
http://www.aliexpress.com/item/5-PCS-LOT-DC-Buck-Converter-15A-10-14V-to-2-5-5V-Peak-20A-High/558859436.html

Rated at 20Amps, ideal for a large car/deep cycle lead-acid battery.

Seems like rather a fancy module on there, no? Well.. it sure is!

Eyeballing the part number it's actually a really high quality DC-DC converter module; the Artesyn "SIL40c-12sADJ-VS", now obsolete.
http://www.artesyn.com/power/assets/lf_sil40c_1208906885_techref.pdf

The module is actually rated at 40A continuous output with 92% efficiency, low ripple, and all the bells and whistles you could want.   Datasheet mentions 18.5A input (@12v) = 222W in and 40A @5V = 200W out, which is 90%, so only about 20W dissipation at full power.  Very nice.  Spec-wise this is far superior to all the other cheapo DC-DC buck converters from china, and a very good price at that.
The modules also support 'current sharing' as well as remote on/off, it's also _very_ well regulated to handle very rapid surges in current (i.e. all your LEDs going from off to on!), and so on.

Quite possibly by just beefing up the PCB traces a little with some thick wire one could get high efficiency car battery->5v @ 40A very inexpensively (about $10 a pop).

Looks very promising!

Caveat: It's possible the modules they're using are rejects but we'll see. They may just available b/c the module's been discontinued.

The three chips on the underside of the host board are a slight mystery; the two on the left look like reverse-polarity protection diodes on the input [update: no, they're P-FETs, only 2mv drop!]  (which I plan to bypass, not wasting my precious juice on them), the other in the middle... not sure yet [update: LM393 comparitor]  The module datasheet implies it's basically ready-to-rock as it comes, with only external smoothing caps.

Note that the module sheet suggests 2000uf output caps for 5v and these have only about 1200-ish, but should be ok.

I'll give more feedback when mine arrive... Excited!

UPDATE 1: DOH! The no-load current is like 290ma @12v!!!! WTF!? Gets toasty just doing nothing. Not so impressed any more. Also at 1.8A output I measured 1A/12.5V in = only 72% efficient. 

UPDATE 2:  Ok so the specs do mention the high quiescent current if you look closely, and if you can live with that the modules work very well; the load regulation is excellent.  It turns out the module does happily output well over 20A (tested at 30A - active cooling a good idea, the small heatsink gets literally hot enough to boil water; thermal cutoff is at about 120C(!) ) - however - the board the module is mounted on has a P-FET for reverse voltage protection on the input and that blows up (quite spectacularly; lets the magic smoke out) above about 15A input current. If you don't care about the protection you can bypass the fet with some (very) thick wire from the input terminals to the module and it works well at very high currents.

Overall it's a pretty good module as long as you're ok with max 13.8v input and wasting a fair bit of power as heat...

Wireless router dropping connection under load - dmesg shows "ath: phy0: Failed to stop TX DMA, queues=0x004!"

Symptom:
Atheros-chipset based router, specifically:

Router Model

Buffalo WZR-HP-G300NH

Firmware Version

DD-WRT v24-sp2 (05/27/13) std - build 21676

Kernel Version

Linux 3.9.4 #320 Mon May 27 02:09:45 CEST 2013 mips

Was dropping wireless connection to my Nexus 7 (and iPod touch) when downloading anything large, e.g. app updates.

Connection would drop on client, interrupting whatever was downloading, then few seconds later would reconnect and continue, then drop again, etc.

dmesg from shell on the router gave me:

ath: phy0: Failed to stop TX DMA, queues=0x004!

every time it dropped the connection. 

cat /sys/kernel/debug/ieee80211/phy0/ath9k/reset

    Baseband Hang: 2538

Baseband Watchdog:  0

   Fatal HW Error:  0

      TX HW error:  0

     TX Path Hang:  0

      PLL RX Hang:  0

        MCI Reset:  0

REALLY ANNOYING.  Lots of internet sleuthing later, I appear to have found a fix!

TL;DR - TRY THIS

Make sure you're not using WPA2/ TKIP mode! Use AES instead - do not use TKIP.

Simply switching from TKIP to AES made the problem disappear completely. 

SO happy about that.

Work for you? Comment below please :-)

Djangoh-my-goodness

Django is good, now I go kick the tires a bit...

Django-cms is absurdly good

Give this guy half an hour to explain why; he sold me. 

Swwwweeee-e-eee-eeet!

Sensor chip w/Active low pin 2 = *NUKE

Maxwell Technologies’ HSN-1000 radiation-hardened Hybrid Nuclear Event Detecto


Kyle : wtf do you use that chip for?
Kyle : bomb warning device?
Dr Tune: no it's to launch a retaliatory nuclear attack
Dr Tune: you hook the active low *NED output (via a fet) to the ignition system on yr ICBM
Dr Tune: optionally you could have a toggle switch or something
 Dr Tune: 4 safeness
Kyle : well at least it triggers on a detonation and not just spotting something in the air
Dr Tune: yeah I wonder how they do production testing
Dr Tune: chips prolly veh expensive
Dr Tune: anyway
Dr Tune: comedic, and I love it just has pin 2 as essentially *NUKE
Kyle : lol yeah
Dr Tune: maybe hook it up to a piezo buzzer or something, so if you don't notice that you've just been nuked, it'll let you know
Kyle : yeah i was thinking its probably part of some sensor network to notify the pentagon or something
Kyle : immediately adjust the defcon level
Kyle : or i guess its not defcon anymore
Dr Tune: ya someone in pentagon has haxored up an arduino
Kyle : go to purple alert or something
Dr Tune: well only what 5 defcons
Dr Tune: so can use an attiny

Snoop NFC RFID card with RTL-SDR dongle

It's been a big year for radio fun!
Playing with NFC / RFID tags recently it occurred to me that the RTL-SDR dongles could potentially be used to sniff 13.56Mhz tags.

As it happens the RTL tuner won't quite tune as low as 13Mhz, but.. the first harmonic at 26Mhz works great!

Here's a Mifare Classic 4K card being repeatedly read by an SCL3711 NFC reader. I wedged an antenna next to the reader, fired up SDR-Sharp and here we go...

SCL3711 reader + Mifare 4k + antenna to RTL dongle

Center signal = 13.56Mhz carrier from reader, side spurs = ASK modulated reply from card :-)

Next stop, demodulation and a nice cup of tea. 

Video:

Addendum - while video shows antenna strapped to the card, this setup seems to receive both card+reader signals just fine from 15 feet away!

Later:  Ok never mind the "15 foot" stuff - not true it seems. Because I was running RTL dongle + NFC on the same PC it was coupling the RF signals through the USB lines, making things look very much better than they really were. I tried tag reading with a non-USB-wired Nexus 7 and the antenna range (for the signal from the card) is as "near field" as you'd expect. So; handy and cheap but not ground-breaking :-)