Monday, January 13, 2014

Thermoelectric cooler Alcohol bath

For the purposes of calibration of temperature sensors at low temperatures or for testing thermo-switches the following layout may be used to make Alcohol cooling bath. The idea beyond using Alcohol is that it has low freezing temperature (-114 C) so it will not freeze in the negative temperature ranges like water which will act like an insulator when it turns into ice. Also, using air as a cooling medium is obviously not reliable because it has low convection heat transfer coefficient, low thermal capacity (and hence low temperature stability), besides the moisture content of air will form frost on the cold sides of the thermoelectric cooler modules resulting in insulation effect.

As you can see in the image above, the insulation cap (on top) not only work as an insulator, but it also prevents the evaporation and loss of Alcohol which has high volatility. 

The cooling capacity may be increased by just increasing the number of thermoelectric coolers (something like the image below). Increasing number of thermoelectric cooler modules for the same path will increase its volume resulting in larger steady state time and may lead to radial non-homogeneity of temperature distribution across the bath.

Friday, January 10, 2014

Stair climbing wheel

This post is just a demonstration for the layout and basic dimensions of a stair climbing wheel. Stair climbing wheels are commonly used in market carts and appliance trucks. There are two types of them: manual drive and motor drive. The later is used mainly in robots, space landers, and some toy cars. 

Stair climbing wheels are (in most cases) only efficient in stair climbing because they are not supposed to turn right or left while climbing stairs. Using stair climbing wheels in carts or trucks (the truck will have two units of wheel cluster) that move on flat grounds is difficult when you try to turn right or left (specially when the spacing between wheel centers are large) because the system will have 4 fixed-direction parallel wheels (imagine a car with four wheels that all of them are aligned and parallel, it will never turn).

Stair climbers should be designed for a given stair step because they will not work properly for any height.

How to make square cavity in ABS plastic sheet

This post is talking about how to make a square cavity cut in thick ABS plastic sheet (or any soft plastic sheet like HIPS). In my case it was 5 mm thick ABS sheet. I needed this when I was trying to make a fixture for a Peltier cooler 40 mm x 40 mm. The tools you will need are almost available at home:

1. Stainless steel ruler
2. Rigid blade cutter
3. Cup saw bit
4. Electric drill
5. Lineman plier (

 Just follow the instructions on the image below.

Wednesday, January 8, 2014

Fair random number generator

When you listen to a list of tracks (assuming you have 100 sound tracks on your pen-drive or CD) in your car and apply the random mode, you will notice that you listen to a specific track more than once per 100 played tracks... Case 1

One day, I was in a training in soft skills and each one in the training was asked to present himself in front of others. So.. for justice and fair, the instructor suggested to assign numbers for the attendant people (13 guy) and use random number generator in Microsoft Excel to select people, so no one will refuse or show complaint. The funny thing was that I was selected for more than 4 times because of such a function and the same for other colleagues... Case 2

Based on the previous cases, this is just a simple VB Macro code for Excel to generate unique random numbers between 1 and 100. 

Sub FairRandom()

Dim final, i, j, top As Integer
last = 1    'Last written cell
bottom = 1    'Bottom value of random function
top = 100    'Top value of random function
For i = 1 To 100000    'For high number of iterations (infinity)
RN = Evaluate("RandBetween(bottom,top)")
For j = 1 To final    'check if the generated random number equals one of the written cells before
If Cells(j, 1) = RN Then
GoTo 1     'if it is duplicated, then don't waste time and check the rest of cells
End If
Next j
Cells(j, 2) = RN
last = last + 1     'Increment last
If last > top Then
GoTo 2
End If
Next i
End Sub

The code results are shown in the first matrix, while the Excel function RandBetween(1,100) results are shown in the second matrix (Highlighted cells in red are duplicated using conditional formatting). 

Tuesday, January 7, 2014

Google OCR test

Today, I was just wondering if I uploaded an image on my blog (via Picasa web albums), will Google make some image processing (for Optical Character Recognition OCR) on the uploaded image or not. I know that Google has an Android application that does the OCR but "on request". If this feature is really available in automatic way, it will make Google image search more powerful and may duplicate search results hundred times. I guess if this process is already applied in Google, each image uploaded will be processed for OCR, then the detected words will be filtered and saved as tags for the picture. It is a difficult process but it is not impossible. 

One of the main advantages of this method that it will help Google in image search by an image so it can find the images even if they are resized, flipped, or converted to gray scale.

For sure, this method may work also for videos knowing that videos are just successive picture frames.

I tried to make an image having a long word of random letters so it will never appear in search results in Google. I tried to search for the written word and no search results were obtained. May be it takes little time to apply the process or update the tags database. I am not going to write down the word because -for sure- Google will catch the image from it.

How to open files on windows startup (Windows Seven)

In this post I am going to tell you simply how to open some files on windows start-up in Windows Seven. For me, I need this in my work to open some excel files used daily in task management, periodic actions, attendance sheet,... etc. Also, I can open internet or intranet pages as well. This helps as a kind of fool-proofing so you will not miss anything.

All you have to do is go to "Start menu", "All programs", "Startup". Then right click on the "Startup" folder icon and click "Open".

Then the folder will open in a new window (notice the long path). Now, you can place (by copy and paste) any file and/or file shortcut you want to open automatically when Windows starts. It is preferred to use shortcuts, so you will not loose your files when you install new Windows.

Friday, January 3, 2014

Smart method to make key panel (board) for offices

This method is a little bit smart to make backup keys for large scale buildings like companies, hospitals, hotels, ...etc. The method is visual and looks like tagging a place on Google maps, so you can easily find the key without following up the name written on the key label. The importance of this method arises in cases where a room has more than one door to access or when there are different rooms of the same functional name. All you have to do is to locate the place you want to find its key on the floor plan, then you will find the key. This method also helps you to recognize visually the missed key.

In this method you can include also keys of closets, drawer units, and electric cabinets, .. etc. As much details you will include, you will need larger panel to make sure that keys are not overlapping.

Also, you can make a fold-able or roll-able versions of this panel so you can save space and hide this backup keys in a hidden place.

Thursday, January 2, 2014

Different Savonius blade|bucket layouts

The following are the different layouts regarding the overlapping of Savonius blades (or buckets). The third layout is the most aerodynamic-efficient layout. It is also the same for helical Savonius wind turbine. 

In layout 3, reducing the gap "b" leads to excessive noise, turbulence, and vibrations, while large gap "b" leads to reducing the effective drag area of the advancing blade. Therefore, the gap should be optimized.