Abstract:

This project is a remake of my greatest college project, the digital voltmeter. This time I made a major modification.

Instead of using a DAC for producing the ramp I used the 555 timer to produce the analog linear ramp voltage for higher resolution. Later I realized that I could greatly reduce component count by using the 555 chip itself as a single slope converter for measuring input voltages.

Voltmeter:

Single Slope Analog to Digital Converter

To understand how the voltmeter works let me introduce the concept behind a single slope analog to digital converter.

The circuit below shows a simplified single slope converter circuit, analog signal to be measured is compared with a linear ramp of definite slope (peak and period). The output of the comparator is therefore a pulse signal whose duty / pulse duration is proportional to the magnitude of the input signal.

To quantify the pulse duration, the output of the comparator is fed to an AND gate. This output serves as a pulse gating circuit for pulses coming from an astable multivibrator. A counter is used to count the number of pulses from multivibrator when the gating pulse is high.

From this we can conclude that…

Vin proportional # of pulses

Vin = scaling factor * (# of pulses)

The frequency of the multivibrator and the slope of the ramp generator are carefully selected to have a scaling factor in the range of x1, x10, x100, x1k, and so on for easier approximation of input voltage without further processing (computation).

A voltage divider or amplifier with controlled gain may be used at the input to limit the maximum input to be equal to the ramp’s peak voltage.

I selected the ramp slope to be 0 – 5V in 500mS. Since I have a four digit display, an overflow of the display will occur on the 10000^th pulse received, this is the maximum # of pulses that should occur while the ramp voltage is climbing from 0V to 5V.

Computing for the Astable Multivibrator frequency…

Frequency = max # of pulses / ramp generator period

Frequency = 10000 / 500mS

Frequency = 20kHz

Gain can be calculated as

Gain = ramp peak voltage / max Vin voltage

Dolly Single Slope Analog to Digital Converter:

I have to ask forgiveness from the entire hobby community for I know LM555 is the most popular IC when it comes to producing a reliable timing. The word “timer” used to be a precise description of this chip but everything changed when I began the remake of my project.

At first I intend to use this chip as a simple ramp generator for my Single Slope ADC but then I realized I could make my circuit much simpler if I reduce the number of comparators.

Using a chip for a different purpose is nothing new to me, and in fact I am known for this habit and this always happen when I get bored. Hehehe.

The “Dolly Single Slope ADC” is centered on the chip’s internal comparator originally intended for voltage control of the output frequency (the one whose inputs are the threshold (pin6) and the control voltage (pin5) ). An external buffer was added to prevent the loading effect of the internal divider network and present a high impedance to the input side.

A constant current source (LM317 but can be implemented using a simple transistor) supplies current on the capacitor to produce the ramp voltage which is compared against the input via 555’s pin6. The transistor Q5 resets the ramp when its amplitude exceeded that of the input voltage.

Another comparator was added because when the 555 discharges it will begin ramping up again at 1/3 of the supply voltage( 9V /3 = 3V), adding an external comparator that triggers at lower voltage (around 1V and can be less) extends the measurable range of the multimeter.

A larger view of the simulation result

The Display:

The display and counter module is based on 74C925 IC (of course anyone can hack a counter or a pedometer to cut the cost further). The rest of the components are trivial.

Experts may find it very useful for rapid prototyping of their design ideas and beginners will surely enjoy the high level approach of programming. It is easy to learn, very straight forward, yet simple.

With all of the advantages offered by Arduino there’s one thing I don’t like with it. The pitch between digital pin 7 and 8 is not standard, and I’ll bet non of the locally available prototyping boards (universal PCB) would be suitable for it.

*Images Courtesy of : Project Blog

At first look the 0.04” offset between a standard header spacing and Arduino is barely noticeable but the problem becomes evident when you try to squeeze a standard spaced shield in. If you do this you’ll probably notice the header’s pin would slightly bend due to the offset.

*Images Courtesy of : Project Blog

For those of who have the luxury of time, the problem can be easily addressed by developing their own shield and go through the pain of fabricating their own PCBs.

Many prefer to buy commercially available shields but the price of those shields maybe far off the budget of a middle class hobbyist. Some will just bend the pins and make it fit on Arduino.

Another solution is we can modify a prototyping board to  make it compatible with Arduino. I prepared a tutorial on how it can be done.

Step 1 – Prepare the Materials

Materials needed for the project are, 1pc e-Gizmo EGPC-02 universal PCB,  2pcs 16×1 female header, 2pcs 8×1 long leaded female header, and 2pcs 6×1 long leaded female header.

You’ll also need a super glue, soldering iron and solder, PCB drill or office cutter, and #20 or #22 stranded wires.

* Prices are true as of 20101013 and may vary depending on vendor and location

**Total Price does not include the price of the tools that will be used and other constructing materials like solders and wires

Step 2 – Insert the Headers

Insert 1 of the 16×1 female header on the universal PCB starting at coordinate B-22 and the opposite end should fall at B-7.

Insert the other 16×1 female header at the opposite side of the board starting at Q-22 and the opposite end should fall at Q-7.

Insert 1 of the  6×1 long leaded header on coordinate starting at R-22 and its end must fall at R-17. Skip 1 hole along column R and insert the other 6×1 long leaded header at coordinate R-15, its end must fall at R-9.

Solder the pins on the opposite side of the board. Don’t be bothered if you noticed that the long leaded headers are connected on the power trace. It is intentional.

Step 3 – Insert the 8×1 Long Leaded Headers

Insert the 8×1 long leaded headers on the Arduino’s Digital IO pins as shown on the diagram below.

Step 4 – Glue the Headers

Insert the leads of the universal PCB we have prepared  at the opposite end of Arduino (Analog Pins and Power Pins).

Using a super glue, glue the pins of 8×1 long leaded header on the universal PCB.

Step 5 – Cut the  Power Traces

If you can recall, we have connected the 6×1 headers on the power trace. Connection between the header’s pins must be cut, it can easily be accomplished using a PCB drill or an office cutter.

Step 6 – Make Connections

Pins of the 16×1 headers must be connected to the pins of the long leaded headers nearest to them.

We can use #22 or #20 stranded wires to make connections between the 8×1 long leaded headers and the 16×1 header.

The 6×1 long leaded headers are connected to the adjacent 16×1 header by soldering.

Step 7 – Connect the +5V and GND

Connect Arduino’s +5V supply pin to one of the power trace (N-12 and M-12, this will become the Vcc of the Proto-Sheild).

Connect Arduino’s GND pin to the remaining power trace (E-8 and F8, this will become the Gnd of the Proto-Sheild).

Finally we’ll have a Proto-Shield that is cheap and can be easily expanded because standard headers is provided (16×1 female header) to allow stocking of additional Proto-Shields on top of it without going through the process of gluing the headers and cutting the power trace.

Below is and example of how DIY Proto-Shields can be stacked. Additional shields require only soldering the long leaded headers on top of it.

One problem I anticipated with using solid wires is that the frequent insertion and pulling out of the wires would wear it especially near the ends. An alternative could be to use stranded wires but using it would be difficult when inserting the wires on the sockets.

After browsing the net I found a topic on how to make DIY Jumper Wires ad this gaved me an idea on how I can create my own version of the DIY Jumper Wires.

Below are the detailed steps on creating the DIY Jumper Wires

Step 1: Prepare the materials

Materials I used are…

* Prices are true as of 20100301 and may vary depending on vendor and location.

Tools I used are Wire Stripper, Soldering Iron, and a Third Hand

Step 2: Extract the pins from the connector assembly

Extracting the pins from the header is not so difficult and in fact there are two methods that can be used to removed the pins from its assembly.

The first method is to heat the pins using a soldering iron until the plastic softens and the pins will just separate or fall out of its assembly. I chose the second method, using a shear cutter we can carefully remove the pins by cutting the plastic that holds them. The second method is faster but there’s a risk of damaging the pins if you apply too much pressure on it.

Same technique was used in extracting the female hirel pins out from an IC socket.

Step 3: Strip the wires

#20 Wires of about 16cm long are cut and ends (about 3mm) are stripped. The more colors you have the better because with it you can easily identify which signal a color represent when everything are jumbled up but unfortunately there are only few colors I found from 3 of our local suppliers.

Step 4: Tin the wires

To make it easier to solder the pins on the wire, wires are pre-tinned

Step 5: Solder the pins to the wires

With the help of a third hand, I was able to solder the pins on the wire very flawlessly.

Step 6: Cover the solder joints with shrinkable tube

I cover the solder joints with a shrinkable tube of about 5mm long to protect our hands from getting scratched by pointed parts of the joint and this also adds professional look on the product we’re making.

At first I tried to use a candle to heat the shrinkable tube but the technique was very messy and dark residue (abo/agiw) was forming on the wire ends. Heating the shrinkable tube with a cigarette lighter worked better.

Step 7: Storing

Finally I finished the DIY Connector . I used rubber bands on both ends to tie them all together.

Building the LCD Projector is a great experience but never was easy. If this is not taken seriously, you might end up with a dead LCD module and lost a couple of bucks just like me.

The principle behind the DIY LCD Projector is fairly simple. If you could remember the days when you’re using the overhead projector for your school reporting, well, the LCD Projector work very much like that same principle. The only difference is instead of using the acetate to project images, on the DIY LCD Projector, you’ll be using an LCD screen. LCD screen can then be connected to a computer to project anything you want.

I got my LCD years ago from Tipidpc.com at around Php1500 (that time LCD monitor still cost around 10 to 15K). The seller mentioned that the displays are OK but are very dim on some parts. I quickly figured out that the problem might be with its backlighting (cold cathode). This is not a problem for my project because I won’t be using any backlight.

Inside the LCD monitor is a control board that converts VGA input signal into a protocol compatible with most LCD modules (LVDI protocol). There are also a few buttons for controlling the brightness, color, contrast, and also for power.

An inverter (below, left) is also an important module inside the LCD monitor. This produces high output voltage enough to drive the small fluorescent tube also called cold cathode (below, right) inside the LCD Module.

Not all LCD modules can be transformed into LCD Projector. Some modules have very rigid connection of its vertical and horizontal drivers that prevents us to open the back portion to be made suitable for projection.

I learned that when I tried it first time. My first attempt was a total failure and I ended up with a damaged LCD Module. The flexible PCB connecting the horizontal drivers got torn apart rendering my LCD Module useless.

The good thing is I still have my control board that I can use on other compatible LCD Module.

I got my new LCD Module salvaged from an old Sager Laptop I bought for Php2000 (whole laptop)

  It is an LCD module produced by LG Philips (Model : LP141X7-C1TO) and I was very lucky that it is compatible with my LCD control board and initial test displayed my desktop image on it.

  I carefully dismantled the assembly of the LCD Module starting from the right side then removed the tape at the bottom.

After all the tapes are gone, I carefully lifted the module off its metal frame and continued dismantling it. It can be easily observed that the LG Philips LCD Module has no flexible PCB that connects the vertical drivers to the horizontal driver circuits which made it ideal for DIY LCD Projector project.

  There are a couple of layers you’ll see after you completely dismantled everything. Starting from the back top there is the plastic frame that secures the back portion and at the same time housed the LCD Module main board. Next to it are the white plastic that reflects the light forward onto the LCD screen. There are two diffuser that sandwiched an acrylic sheet. Well, none of these elements are important because it’s only the LCD screen we’re gonna use.

I ran a few test just to make sure my setup is still working after I did all dismantling stuffs and the picture below shows how it is look like.

I housed the main control board inside an Alexan enclosure.

The DIY LCD Projector worked perfectly fine especially under a dimmed light condition.

  I added some box and fan to allow heat to circulate below the LCD screen because the project gets hell hot when operated continuously.

What happened next? I got my DIY LCD Projector working for 15mins  but too bad when I needed to fix something I have to disassemble everything and when I powered the setup again I got the LCD Module to main control board connection inverted. This damaged my 2nd LCD and taught me another hard lesson.

For those who would like to try building this one, please be very careful so you wont suffer the same fate I had. Happy hacking….

I played it for a while but then I got a little bored so I finally decided to crack it open.

The toy is powered by four small button cells. Two of the cells power the motors while the other two power the control board.

Opening the toy was quite a bit tricky. The track belt needs to be removed first and the middle wheels must be pulled out to reveal the two screws joining the tank’s upper body to the lower chassis.

Inside it is a little circuit board centered around an SMT IC. Guess what it is, a microcontroller? Eeeeeh!!! You’re wrong. It is controlled by a dual comparator IC which is pin to pin compatible with LM358 (the body marking says it’s “0358”).

Inside the gearbox are two small DC motor no bigger than a cellphone vibrator motor that differentially drive the tracked wheels and, of course, a couple of gears.

Optical sensors are located at the bottom. The main part are the phototransistors (dark part) that detect the reflection (indication that the surface is not black) of the light emitted by the red LEDs (transparent part). The outputs of the comparator provide the drive signal to turn on/off the motors of the tank.

The main switch is also mounted on the component side of the board.

It was easy to trace the circuit’s layout since few component resides on the circuit board. Looking at the circuit, we can clearly see a window comparator that turns either of the motor off when the voltage produced by the phototransistors divider network goes beyond the window voltages (most of the time phototransistors are shorted but it opens when it senses a black line).

When I return I’m hoping I could finished those projects I already started. I’m also excited to start working with my thesis starting this summer.

Thanks for visiting my blog…

Can you remember the movie “Entrapment” wherein the lead actress (Katherine Zeta Jones) tried to defeat the security of the building to get a very valuable item? In the movie she had to practice very well only to cross an area guarded by invisible lasers that once the line is cut it would trigger the building’s alarm and that would alert the all the building’s guards. Hollywood spy movies have given those optical alarms (infrared laser) an impression of being a state of the art technology. Though in reality it is very simple, it is still one of the projects many hobbyist would love to build.

On my CIA project I’d like to show how simple (6 components, an alarm clock, and a laser pointer) it is to build one of these devices.

Schematic Diagram…

Circuit Description…

The circuit is basically a monostable multivibrator (active high) compost of resistors R1 and R2, capacitor C1, and the diode D1.

The phototransistor Q1 act as triggering device that at normal condition pulls the anode of D1 to ground when there is light (coming from a laser pointer source). This would divert all the current flowing across R1 to the ground. The value of R1 was carefully selected so it would dissipate power as low as possible since it is supplied by a singe 1.5V cell.

If the light entering the phototransistor Q1 is blocked, the phototransistor would open and this would allow the current to flow through D1 and therefore will charge the capacitor C1. The voltage across the capacitor will increase until it can produce enough potential to drive the transistor to turn on.

The transistor Q2 inverts the signal from the monostable mulivibrator and because the Alert# pin is active low this would set the clock’s alarm when it is pulled to ground.

If the blockage is removed, the light would trigger the phototransistor again and would pull R1 current to ground. At this point the capacitor will stop charging and will now enter discharging phase. Energy stored on the capacitor will slowly discharge through R2 and the transistor Q2. Voltage at the capacitor will slowly decay and there would be a point where it can no longer produce enough current to drive Q2. Q2 will then turn off and this would also turn off the alarm.

I measured the time the alarm will stop after it was triggered and I measured a considerable period of 1.5 minutes. This period can be easily increased by increasing the resistance value of R2.

C2 capacitance may also be increased to increase the alarm period but this would also slow the charging time down. If this happens, the sensor’s sensitivity may be affected. In order to correct this, the value of R1 can be lowered.

Construction…

I first constructed my circuit on a breadboard to quickly test if my design concept will work on actual. Using breadboard also allowed me to easily trim the component’s values to achieve desirable response.

After successful testing I finally decided to assemble it on top of the alarm clock’s board.

Care must be taken so it wont interfere with other components originally there. I also have to strip a few parts only to make the circuit fit inside.

Bill of Materials…

* Prices are true as of 20091001 and may vary depending on vendor and location.

** Total Price does not include the price of the tools that will be used and other constructing materials like solders and wires.

The total price does not include the price of the alarm clock and the laser pointer because it varies greatly depending on the vendor and location. I bought the alarm clock at an Ukay Ukay store for only Php 37.00 bringing the total project cost to Php 57.00. Daiso sells these clock for only Php 66.00. Cheap laser pointers may be bought on stores along Quiapo for as low as Php 30.00. I bought mine at Shopwise Cubao for Php 90.00 (with LED flash light).

Conclusions…

I spent almost a lifetime designing circuits for high voltage sources (minimum of 5V) and never thought designing a circuit for 1.5V source would give me great challenge and more learning. At these voltages the effect of diode drops and the parasitic resistances becomes very significant.

Results of my simulations were far from the actual response, nevertheless my circuit worked perfectly.

Right now I have plans to assemble my CIA version 2. Yes you heard it right, I already designed version 2 and I’m very excited to blog about it. It is already working on my simulations.

Improvements are to use infared light instead of ordinary red LED and it is also capable of accepting a pulsed light for greater efficiency and would prolong the battery life of the light source.

Some say it is possible by travelling at speeds faster than the speed of light. But then physics also limits a massive body to travel or even approach speeds near that of the light. I did my own research and results were very shocking. On my realization I said to myself, what the hell’s wrong with them? If they want to turn the hands backwards all they need to do is to make it turn “counter clockwise”. Hehehehe.

For details about how to disassemble a desk clock, kindly visit the blog post below…

What’s Inside It? Analog Desk Clock 

At first I thought this would be very simple. I thought interchanging the connection of the wires connected to the solenoid would reverse its polarity and thus could make it turn counterclockwise. The solution didn’t worked because when I looked at the pulse on scope it was AC alternating its pulses every second. Interchanging the connections wont cause anything because AC don’t have polarity.

I also tried mounting the solenoid on different orientation but the scheme didn’t worked either. I theorized that there is something with the assembly of the iron core that makes it turn in one direction.

Just when I almost discovered the solution myself, uncle google guided me to a link on instructibles on how to turn it backward. (darn it, why is there always someone stealing my ideas, hehehe)

The guy’s solution is very elegant and simple. All we need to do is to remove the iron core, flip it vertically, then assemble all the part back together again.

Before inserting it back on the case, I ran a minor test to make sure its working before all the screws are back on.

Surprisingly, it worked!!! The project is now ready for full assembly.

Below is the video of the fully assembled time machine.

I found my cheapest clock at Daiso for only Php 66 (actually I found the cheapest 4hrs later at an Ukay Ukay store around Araneta for only Php 37).

This nice clock has a cover that doubles as its stand.

Opening…

The analog desk clock has four screws that can easily be opened using standard phillips screw driver.

Inside it is a generic clock box you’ll see on most desk clock of this size.

To open it further you must remove the Alarm and Time setting knob first.

Then you can force it open by sliding the precision screw driver on each of the four locks. Locks are located on each sides, one on top, and one at the bottom just above the battery compartment.

Dissecting…

I have opened many of these clocks (cheap and classy, China and US made) before and noticed that the internal assembly is somewhat generic. The only difference you’ll notice is the materials that were used. Sometimes the buzzer is also mounted on board. And, placement of the stand offs may vary depending on its manufacturer.

None the less, if you take out a control board from one clock, chances are it will fit on another clock.

The control board seems less hack friendly. Only three components are mounted, namely the solenoid coil,  buzzer, and the crystal resonator. The alarm is triggered by pulling the trigger pin to ground.

Clock are pulsed by a current alternating its direction every second across the solenoid. The whole circuitry are supplied by a single alkaline battery rated at 1.5V.

The flash drive has no screws and once you opened it, there’s no way of putting them back together again.

Model:

Unknown (CDR King 1G Flash Drive)

Specifications:

Green Color

Mini Size

1G Bytes

The USB flash drive is powered by UT163 controller from USBest. It is running on 12Mhz Crystal with very few supplementary components.

The flash is located at the back and fits perfectly for the small enclosure.

The USB flash drive has very few components and compost mainly of resistors and capacitors (probably for the controller housekeeping). A green LED is provided to indicate controller’s activity.

After opening it I quickly noticed the burned (and bloated) section on the controller that rendered my flash drive useless. It is no longer repairable but I was hoping data could be recovered if flash will be transferred to another good flash drive.