Unmanned Rig

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The last project of my undergraduate life was an industrial embedded system. Wabco, a major hydraulic system manufacturer, wanted a system that would continuously monitor a testing rig. Testing rigs are those machines that they use to test the hydraulics and this involves pressure and temperature parameters. The system should be able to monitor these parameters for sustained periods of time (24X7). The operator is required to give lower and higher threshold values for each parameter at the start of a testing cycle and then the system measures the parameters to see if they are within the 2 thresholds. If not, then there is an abnormality and in the event of any abnormality, the system should report it to the operator through a SMS and stop the rig. For completeness, the board has a display that sequentially displays the parameter values. The embedded system is designed to handle 6 pressure values from 6 pressure transducers and 2 temperatures from K-type thermocouples.

A major feature of the board is an indigenous solution to a local problem we have in Tamil Nadu – power cuts. The board is designed to detect these power cuts and intimate the operator and when the power resumes, the rig is automatically restarted without manual intervention – automation.

The major components of my design were an MSP430G2553 microcontroller (for central processing), an ATMega16 microcontroller (to provide display data for the 7 segment displays through IC7447 decoders), a GSM module interface (to send the SMS), a MAX4617 multiplexer (to channel the 8 sensor values), a relay (works in tandem with the rig’s control switch to stop or start it) and on-board power regulators for the power supply. After the schematic development, PCB layout & manufacture and assembly of components – the result is:

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The embedded system’s top side (above) and the bottom side (below)

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For ‘industrial reasons’, I wasn’t allowed to take my phone to record the video of the board working with the rig, but here is the next best video I have – the testing of the board with 1 pressure and 1 temperature monitoring.

The curious thing about doing an industrial project is preparing and analyzing FMEA – Failure Mode and Effect Analysis to evaluate the performance of the system. This is my FMEA for the Unmanned Rig

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HP07 Digipot Interface Module

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This is the first product design work that I have done and I did it for the auxiliary project (also called mini-project) required for my bachelor’s degree in my 7th semester. From the outset, I had one idea set firmly in my mind – “my mini-project should be a mini-product”. So, I wanted to create a module and spent 2 months designing an RF transceiver. In the very end, I realized I couldn’t fabricate it at home and had to scrap that idea. But, I was certainly not gonna back out and then this one came to me.

This idea is an interface module for digital potentiometers. Digital potentiometer ICs are those which enable you to control a potentiometer (simply a variable resistance) digitally. It is used in applications like digital control of an amplifier’s gain (especially for instrumentation, isolation amplifiers), voltage references etc. The snag is, most common digital potentiometer IC’s use an Up/Down counter interface that many hobbyists would need time to get around. So this module is designed to provide a selectable parallel/serial interface to the user. Also there is an on-board DIP switch that can be used to set a resistance directly. For example, if I had a mechanical potentiometer and wanted to set a particular resistance, it would be impossible to do so without measuring it. In this module, if you provide the correct binary code on the DIP switch, the resistance is set to that value automatically.

This article is about my experience of the ‘product development life cycle’ that was required to make a working prototype of the module. In the beginning, I spent a couple of days on finalizing what my module should have and should do. Once I settled that, I chose to use the ATTiny861 micrcontroller as the brain of the module. Then, I began writing the code for it and simulating it in Proteus. After several bouts with the USI (Universal Serial Interface), PCINT (Pin Change Interrupts) and WDT (Watch Dog Timer), I finally got a working version of the program in simulation.

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Then came the breadboard where I soon realized that the simulation wasn’t exactly accurate. I had to make subtle changes to perfect the design. Over the course of another day with repeated testing (using the NI myDAQ), I completed and finalized the complete working version of the embedded C code for the microcontroller. Subsequently, the schematic or circuit diagram was also finalized.

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The next step in the design process, is the PCB design. Since, I was creating a module, I wanted the PCB to be very compact and dense. I ended up creating a 34mm by 42mm double layer board using EagleCAD and the layout looked like this:

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After this comes PCB fabrication and I did this in my own ‘facility’. I printed of the two layers of the PCB and transferred the routes to a copper board.

20151015_185832Since it is a double sided board, I transferred the top layer on one side of the copper board first. Used that as a reference and drilled necessary holes onto the board. Now I aligned the copper board holes with holes on the bottom layer paper and then transferred the back layer as well.  The  Toner transfers are not always perfect and so after some heavy correction work, this is what the bare board looked like:

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Since I have already written an article about PCB Fabrication at home, I am gonna skip past that. But just for the sake of mentioning, the process continues with etching followed by mask removal, trace corrections, via connections, tinning of pads, component assembly and soldering (simultaneous trace and continuity corrections too). After a lengthy spell of hands-on work, the module was finally complete.

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Now, the last phase of design – final testing. I connected the P/S mode select, DIN and CLK pins to the myDAQ for providing the necessary signals. I also used the myDAQ for measuring the resistance similar to the way I tested the breadboard version.

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And to my great joy and disbelief, it worked. Here is a demonstration video:

Thus, I finished my very first product. I went through all typical stages of a product design and now I am generating the gerber files to have it manufactured and eventually sell a few, if possible. Since no true design process is complete without documentation (ofcourse I wasn’t gonna leave that), I have attached my user manual for the HP07 Digipot Interface Module.

The Electro-Mechanical Clock

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This project essentially brings together what I have done separately in different works. It was nice fun to do an all electronics project like a full fledged digital clock or a PCB and also a heavy duty workstation made from wood. But the real fun begins when all that is put into one project.  I love both electronics and mechanical engineering and so I wanted make something that portrays the importance of time and also the essence of electronics and mechanical and there came the Electro-Mechanical Clock.

A clock because, as far as I am concerned, time is the most important quantity. This clock contains almost everything – microcontroller, transistor, IC, LED displays, resistors, capacitors, inductors and circuitry done two ways, both as a PCB and also the traditional wired way.

To go with that, there is also a gear assembly and a roller bearing (two gems from the mechanical world) and not to forget the electrical – a transformer and a DC motor.

From gear design to PCB design, this project demanded everything I have. This is just the introduction to the 24 steps it takes to make this. Check it out: http://www.instructables.com/id/The-Electro-Mechanical-Clock/

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The time was 8: 10!

The movement of the gears:

The minutes counter:

Making PCB’s at Home

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A PCB (Printed Circuit Board) is arguably the highest form of fabrication in the field of electronics. It was once a thought that it is almost impossible to make them at home but later Ferric chloride etc. were used. But Ferric chloride isn’t a commonly available chemical in a locality. So this article is about how you can make your own PCB with easily available materials.

To start off, you need to generate a PCB layout. There are many softwares available but I suggest using EagleCAD from Cadsoft. It’s easy to learn and has everything a hobbyist would ever need. The following are useful links to learning the software:

Once you have a layout, like this one (I constructed a 555 astable multivibrator PCB).

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Now in Eagle’s print dialog box, you will find options like black etc. We want the print to be in black so tick it. For all PCB implementations keep the scale to be 1. Use glossy paper like magazine paper and print the PCB layout using a Laser printer only. Cut it to suitable proportions. The only high profile thing that you will need is a copper clad board. But you can get that easily these days at ebay.

Keep the printed side facing the copper and simply iron it. Keep the iron box over the paper and board, to heat it. As you heat it, the laser toner (which is like a plastic material) will melt and get stuck onto the copper. Be careful not to move the paper over the copper and smudge the ink. Do it as gently as possible and repeatedly just press over the paper. Also, never leave the iron box over the paper and board. Do that for about 15-25 times and after you are done let the board cool down before carefully remove the paper. It should come off easily but if it doesn’t come off use water to rub it off. Don’t rip it out. Once you are done with it, you must end up with something like this.

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If all this seems too ‘out of hand’, you can simply draw your board with your hand. Use the layout as a reference and sketch it on the board with pencil (and scale too!). Then use a permanent marker to simply draw the board. If you draw with your hand, the circuit lining will not be perfect but you can get the job done easily. The advantage with permanent markers is that you can also add your initials like what I have done.

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Let it dry overnight and meanwhile we can prepare the etchant. The etch process can be described as follows. The laser toner or the permanent marker transferred onto the copper serves as a mask. The etchant acts on copper and dissolves it. So all the surrounding copper is dissolved except the one underneath the mask which gives the required copper lining. Usually Ferric Chloride is used for etching but its often difficult to get it and it is also relatively costly to the current method.

The etchant I have used is a mixture of conc. Hydrochloric acid (which every household has) and Hydrogen Peroxide (I got it for Rs. 20 from a medical shop). The key here is the pH of the solution. If the concentration of acid is too high (pH<1), the copper etching will be too aggressive that the mask will  be rendered useless and if it is too low (ph>3), the etching will take ages to complete. So, the optimum level is to use 1 part of conc. Hydrochloric acid (pH < 1.1) with 1 part of Hydrogen Peroxide (ones sold in medical shops are 2% solution, so the extra water will dilute the acid suitably). If by variation of some quantity, the etchant fumes (still very concentrated), carefully add water by drops along the side of the container (to avoid a rapid increase in exothermic enthalpy). Keep adding until the etchant just stops fuming. But this involves keen observation, so if you are a starter stick with measurements and be extremely careful while pouring the acid!!!!

Use the board only after it has completely dried. Then wrap the board with wire to serve as a holder. Make sure that the metal in the wire never comes in contact with the etching solution. Then just immerse the board into the etchant using the wires and make sure the board is completely immersed in the etchant.

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Now all you have to do is agitate the solution every 5 mins or so. Do so gently because you don’t want anything coming out of that container.

Within 5 minutes, you must observe a nice turquoise (blue-green) color. This is due to the reaction between hydrochloric acid and the unmasked copper with hydrogen peroxide as the oxidizing agent. This results in the formation of copper (II) chloride. For people interested in advanced Inorganic chemistry – Copper tetrachloride ions also play a role as a mediating agent.

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After about 15 mins with constant agitation in regular intervals of time, the board will becomes something like this. 

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Keep observing, don’t let the board simply rest in the solution for a long time. Remove the board as soon as the etching is complete. A complete board should look something like this.

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Remove the board carefully, dripping any remaining solution back into the container. Do this near a sink and wash the board with excess of water under a tap. This is to drive off any remaining etchant on the board and wire and then dry the board.

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One the board is dried, we need to remove the permanent marking. Again we use a commonly available material – nail polish remover. The cheap ones will be more than sufficient. Add drops of the remover on the board, it should start dilating and the copper should be visible.

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Rub the ink and it will be removed. Do this with some gloves, so that ink does not stick to your fingers. Once you have all the ink removed, you will still have the laser toner (only because I used that too, not if you use only permanent markers). Use steel wool (steel rug used for dish washing) and carefully rub of the toner while having the board under a steady flow of water from a tap. Dry the board again and you must have a raw PCB.

To make things a little attractive, print another image (preferably color) of the layout and cut it to the same dimensions as the board. Stick the printed  paper on the non- copper side of the board. if your measurements are correct, the copper linings underneath will exactly coincide with the printed content on the non copper side.

Drill holes wherever necessary either using a drill machine and fine drill bits or a PCB hand drill. A drill machine (the one I used) costs a lot and I got the fine drill bits – 0.6 mm, 0.8 mm & 1 mm from ebay. If you are not gonna use a Drill machine for anything else, don’t buy it. Instead go for a hand drill also available at ebay since it is significantly economical. Once the holes are drill you have a complete PCB now.

Non copper side:

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Copper lining side:

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If the holes vary by a little, it can be rectified during soldering. If the variation is large then you got your measurements wrong.

Now all that remains is to add the components and solder it. While using IC based circuits, it is better if you use a IC holder rather than soldering the IC directly. Soldering is arguably the toughest part because it requires a lot of skill. But like everything else it is attainable by practice.

After soldering:

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The shiny powder like thing in between two solder joints is not lead, its actually the reflection of the plastic which slightly melted while soldering. A tip while soldering is to scratch the copper junction  and the component terminals with a sharp object. This removes the oxide coating and also enables the lead to adhere strongly with the copper and the component. As you can see I am not great at soldering. But as long as you can get the junctions in proper electrical contact  without short-circuiting (especially near the IC holder pins which are very close to each other), it is more than enough.

The finished neat PCB with components:

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You could attach a battery holder with it and make it a self containing board, but I coupled it with a breadboard using the soldered wires.

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When you switch the supply on (5V), the LED blinks and you know the circuit is working correctly and there is nothing wrong with the PCB or the soldering.

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I have uploaded the video of its ‘blinking’ operation. Do look at it and my other circuits too!

There are actually hundreds of ways of making PCB’s but I hope you find this one useful too. Good luck for your circuits!