’s dumpster dive

Sparkfun’s dumpster dive is once in a few months event when they prep a limited amount of red boxes filled with rejects and some left over that they don’t feel as retail quality merchandize for various reasons, and put them on sale.

I bought these boxes on two occasions so far and I am reasonably pleased.
Let me share my experience.

  • Sale.
  • The sale takes place on select Fridays. In both occasions I learned about the sale when I visited the site to check out their blog section for new products, which they announce on every Friday morning.
  • The sale event will occur at 12 noon MT.
  • The whole lot will only last a couple of minutes, then the sale will be over.
  • Prior to Noon, you go to the site, login and go to the product page(DD-12012). There is no purchase button displayed yet. Precisely at 12 Noon, you start hitting the F5 key to refresh the screen. Once you see the Buy button, click on it to secure your purchase. If you can go through the purchase process in less than 2 minutes (confirming your address, shipping method and payment information and so so on – the fact you are already logged in will help expedite the process), chances are you will be rewarded with the order confirmation page.
  • Wait with a great anticipation for 3~4 days for the box to arrive.
  • Open the box and find out what is in there.
  • First purchase. (Feb 2014) – All parts listed were confirmed functional.
    • Pcduino v1 x1
    • PIC KIT2 compatible CANAKIT programmer x1
    • Vehicle diagnostic kit x1
    • Sonar module x2
    • FTDI USB-Serial converter (3.3V) x1
    • Stepper motor driver board array. I was able to separate 5 good boards while destroying 1 using dremel
    • A lot of electrolic capacitors
    • One comparator, One photo interrupter, One gap sensor, One ADC.
    • Half dozen of banana plugs
    • USB bluetooth dongles.
    • 3 pin rotary encoder x1
  • Second purchase
    • LCD module 24 chars x 2 lines
      It had 14pin connector. Using Arduino example sketch and pin out information I gathered from Internet, The module was confirmed functional. There is a two terminal pad on PCB which is obviously for backlighting and it looks like EL lighting. $10 value.
    • LCD module 16 chars x 2 lines
      There was a 14 pin ribbon cable coming out from the module. Again I used the pinout and Arduino Uno to confirm the functionality but this one did not work at the first time. It turned out the ribbon cable was broken, so I removed it and replaced with a header connector. The part is now working. $7 value.
    • Bleep drum version 1
      1) This assembly was in a bad shape. I suppose the kit was used in a class room environment or something, but who ever built the kit got the switch and stereo plug on the wrong side of the PCB and must have abondned the project. 9V battery holder and one of four studs were missing as well. Desoldering those multiple lead components was not a fun at all.
      2) I attached 9V battery and powered it up, hoping the LED will light up. Nothing happened and 78I05 was getting rather hot. Quick check on the output of the voltage regulator indicated something was loading down the VR really bad. Pop out the 8 pin dip and LED started to respond to button pushes. VR out was 5V. Oh, bad IC chip I thought and looked a t the part number on it. This is where real shocker camein. It said TA7015D, which is audio Amplifier. Wait a minute, the schematic I found on the Internet says this should be 4901 DAC! Both are 8 pin DIP IC but was the kit supplied with the wrong IC chip?
      3) So I replaced a chip with 4901. I purchased it from when I ordered other parts. Now it seems to be working $50 value?
      4) If the kit was supplied with a wrong chip, then the poor guy who attempted to build it had no chance of this working.
      5) I also feel bad for people who is coming to electronic kit building these days. In my days, components were large. Solder pads were large and solder melting temperature was low due to lead in the solder. It is more difficult to work on PCB soldering even for me who I consider somewhat experienced in soldering.
      6) Bleep Drum is fun!
    • LPC 1768-H blue board
      1) This is a retired Arm cortex board on Sparkfun site. NGX saite is still selling it for $50 or so.
      2) When powered, the test LED was dim and there was no initial booting action where the LED was supposed to blink four times. Scoping the LED output confirmed it was blinking too fast. Somebody must have tried to download a blinky program but with a wrong timer value.
      3) I tried to connect to UART0 with USB-serial cable (using just black-GND, Green-RX0, White-TX0, no connection to red wire) connection after downloading flashmagic. Rebooting while sw press started a bootloader and I was connected. I reinstalled USB secondary bootloader.
      4) Now the USB bootloader started to work. I was able to drag and drop the initial bin file to the board. The board is now reinstated to its original shape. When powered up, LED blinks four times and wait to be programmed.
      5) But I don’t think I keep looking at this board because these days there are so many other options to jump into Arm micro controller more cheaply and easily . I am experimenting with FRDM-KL-25Z with mbed tool chain and its incredibly easy to use. Cypress PSoC now sells $4 board that comes with USB serial interface that can be snapped off for dedicated USB-UART cable afterwards. What a world are we living in?
    • Atmega 328P DIP
      1) Pins were all mangled up so I need to straighten them using a pair of tweezers. Popped into ISP programmer that I hacked with Arduino nano but AVRdude can not read the content. Its either a)broken, b)fuse is configured so can not be programmed without paralell programmer or c)fuse is set to use external crystal.
      2) Out of whim, I popped out the 328p from Arduino uno that I had and placed the 328p in question into Arduino board, loaded the blinky program and on-board LED started to blink. So this must be a 328p with arduino bootloader preloaded. $6 value.
    • More Atmega micro controllers (4 of them)Those are all SMT components. I probably would not be able to use them
    • SC300 wifi module x5
      This looks fantastic but I don’t know how I can use them in this SMT pinouts.
    • Header pins.I received about two dozens of solid header pins. It turns out a perfect fit for my NRI (National Radio Institute) Lab Trainer’s terminal pins which were too loose to connect jumper pins to. So I broke up these header pins to single pins and soldered on top of terminall pins on my trainer. Now the jumper wires slide into it very snuggly. The 35 years old electronics lab trainer regained a new life. Nice.

Will I try the dumpstar again? Maybe I will. The process of troubleshooting seemingly non-working product has some attraction in it.

ハノイの塔を解く(Solving Towers of Hanoi)

ハノイの塔というのはパズルだが、リカージョンというアルゴリズムによくなじむのでプログラミングの教科書に出ていることがある。 自分がこれを見たのは”Oh Pascal!”というパスカルの入門書で30年くらい前に発行された学生向けの教科書だ。


これをコンピュータープログラムを使って解くとどうなるか、という話である。 パターンを見つけるために少ない枚数で実際に解くことを試みる。

Move(1disk from A to C) = Move a Disk from A to C


Move(2disks from A to C) = 
 Move a Disk from A to B
 Move a Disk from A to C
 Move a Disk from B to C

ここで棒Bを使うことになる。 つまり、まず上の円盤を棒AからBに移し、下の円盤をAからCへ、最後にBに移してあった円盤をCに移して完成だ。

Move (2 disks from A to C) = Move (2 disks from A to C using B)

3枚はどうか。 すでに2枚を動かす方法はわかっているのその方法を使ってまずは2枚をBに動かしておき、最後の一枚をAからCに移動、さらに2枚を動かす方法を使ってBからCに移動するという方法で動かせる。

Move(3 disks from A to C using B) =
 Move(2 disks from A to B using C)
 Move a disk from A to C
 Move (2 disks from B to c using A)

4枚の場合も同様に考えられるのでパターンとしては (n-1)枚の円盤をAからBに移す。最後の円盤をAからCに移動し、その後(n-1)枚の円盤をBからCに移す。 ということになる。

Move (n disks from A to C using B) =
 if n>2 Move (n-1 disks from A to B using C)
 Move a disk from A to C
 if n>2 Move (n-1 disks from B to C using A)

このパタ-ンを使って関数を書くと、自分で自分自身を呼びだす関数になる。これがいわゆるRecursion と呼ばれるプログラムテクニックだがCでもPascalでもPHPでもいまどきのプログラムなら軒並みサポートされている。ただし普通のループに比べるとスタックにどんどん自分のコピーを積んでいくためメモリーを消費し、昔の8ビットパソコンでは何せRAMが32キロバイトあれば高級機、計算しているうちにメモリーが足りなくなる、なんてこともあったりして、Loopで記述できるものはRecursionをさける、というのが常識だった。

function Move (n, from, to , using) =
 if n=1 "Move a Disk from 'from' to 'to'"
 Move (n-1,from, using,to)
 "Move a Disk from 'from' to 'to'"
 Move (n-1,using, to, from)

Free Pascalで書いた例

program hanoi;
             {Recursively solve the towers of Hanoi problem.  Moves disks from A to C.
             The code from "Oh Pascal" by Doug Cooper}
var height:integer;
  procedure Move (Height: integer; FromPeg,ToPeg,UsingPeg:char);
    if Height = 1
    then writeln('Move disk from ', FromPeg,' to ',ToPeg)
    else begin
      Move (Height-1, FromPeg,UsingPeg,ToPeg);
      writeln('Move a disk from ',FromPeg,' to ',ToPeg);
      Move (Height-1,UsingPeg,ToPeg,FromPeg)

  writeln('How Many disks are you going to start with?');
  Move (Height,'A','C','B');


#include < iostream >

using namespace std;
void move(int numberOfDisk, char fromPin,char toPin,char usePin);

int main() {
    int numberOfDisk;
    char fromPin = 'A',usePin='B',toPin='C';
    cout << "How many disk do you want to move from pin A to pin C?: " ;
    cin >> numberOfDisk;
    move (numberOfDisk,fromPin,toPin,usePin);

    return 0;
void move(int numberOfDisk, char fromPin,char toPin,char usePin) {
    if(numberOfDisk == 1) cout << "Move a Disk from "<< fromPin << " to " << toPin<< endl;
    else {
        cout << "Move a Disk from " << fromPin << " to " << toPin << endl;



'''Towers of Hanoi'''
def move(numberOfDisk, fromPin, toPin, usingPin):
    if (numberOfDisk == 1):
        print ("Move a Disk from ",fromPin," to ",toPin)
        print ("Move a Disk from ",fromPin," to ",toPin)

if __name__ == '__main__':
    numberOfDisk = input("How many Disk would you like to move? ")

Python で円盤の数を4とした場合の実行例

~ $ python3
How many Disk would you like to move? 4
Move a Disk from  A  to  C
Move a Disk from  A  to  B
Move a Disk from  C  to  B
Move a Disk from  A  to  C
Move a Disk from  B  to  A
Move a Disk from  B  to  C
Move a Disk from  A  to  C
Move a Disk from  A  to  B
Move a Disk from  C  to  B
Move a Disk from  C  to  A
Move a Disk from  B  to  A
Move a Disk from  C  to  B
Move a Disk from  A  to  C
Move a Disk from  A  to  B
Move a Disk from  C  to  B



Python version で試してみると、手持ちのややくたびれたノートブックパソコンではステップの出力が終わるのに 円盤の数が23枚で30秒、24枚で1分、25枚で2分かかった。(下の出力結果参照)実行時間がここの調子で倍々で増えていくとすると入力が64枚のときに解法を出力するのに2の38乗の分がかかるということになるが、これを年に直すと、なんと52万年というとんでもない数字になる。 ので上のプログラムに64と入力しようものなら計算が終わらない。 なるほど、これでは世界が滅びるわけだ。

~ $ time echo 23 | python3 >/dev/null
real	0m29.308s
user	0m29.225s
sys	0m0.054s
~ $ time echo 24 | python3>/dev/null
real	0m58.437s
user	0m58.237s
sys	0m0.122s
~ $ time echo 25 | python3>/dev/null
real	1m55.068s
user	1m54.540s
sys	0m0.320s

Hiding SharePoint list column from list view

This article is about a JavaScript snippet that hides a specific column from a SharePoint list view. If I google this subject, most of the articles found on the Internet is about hiding a specific column from new, display or edit form. Although Javascript can do this, you can do the same thing without use of JavaScript by enabling list content-type as well. See here.

Not many articles talks about hiding columns from the list view though. (This one is an exception)
The link above shows the solution for toggling the particular columns. I only needed to hide a column from the list. But why do I even want to do that when one can simply create a view without that specific column you don’t want to see?
The reason is that I want to show the list based on filtered value from the column in question. I can add the filter webpart that I can connect to the target list, then specify the column to which the filter webpart will be connected to. In another word, for the filter to work, the column need to be a part of the list view (This is no longer the case with SharePoint 2013 or SharePoint online.  See below). Since the column will always show the same value for all displayed items(filtered value) I want to hide this column. If your company allows the use of SharePoint Designer, then you can use the Dataview webpart where you can use the column that is not shown to filter the items list. But Dataview creation and editing requires SPD. I wanted a easier solution, hence this javascript snippet.

if (typeof jQuery === 'undefined') { throw new Error('hide column snippet requires jQuery') }

//This function gets targetTable object and columnindex to hide
//targetTable is a jQuery object with single element.
function doHideColumn(targetTable,col) {
    targetTable.find(".ms-viewheadertr >*[class^='ms-v']").eq(col).hide();
    targetTable.find(" >tbody >tr").each(function(){$(this).find(">td:eq("+col+")").hide();});
$(function() {//this hide the colName column from all table in the page
    var    colName="colToHide";
    var    tarray=$(" th:contains('"+ colName +"')");
    var    tlength=tarray.length;
    var    colindex;
    for (var i=0; i<tlength; i++) {
        doHideColumn($(tarray[i]).closest('.ms-listviewtable'), colindex);


This code snippet requires jQuery. You can use content editor Web Parts (CEWP) to include this code (don’t forget to wrap the code with script tag.) It works with SP2007 (My office’s current version) I may need to look at the code again when our IT upgrades the server to either 2013 or O365.  *Edit*  On SharePoint 2013 and SharePoint online filter can be applied to any list column regardless of if the target liist view contains the filtered column.  Therefore, solution explained here is unnecessary. *end Edit *
The code above scans the entire page for column headers with “colToHide” name and hide the column. (or columns if there are multiple lists in the page and if they contains the column with same name)
Since this code uses jQuery array object to hold the column information, it wont be difficult to modify the code to accept more than one column names to hide multiple columns from single list. For now, this snippet achieves what I need.

Filter Web parts are nice. For instance, URL query web parts let me create a page that contents are based on the filtered value in url query. For instance,
both link goes to the same page but the first link will show project phase 1 list items where the next link will show project phase 3 list.