Homemade igniter

My sons are a week off from school and since it was rainy we decided to make an igniter for fireworks or model rockets. The type of igniter that we made comes fromĀ Grant Thompson “The King of Random”. He entertains an excellent YouTube channel with lots of great experiments with simple materials. The igniter is easy using only some stranded copper wire, matches and tape. The stranded wire is stripped and a single copper strand is connected to the another wire. A match is then placed between the two wires and the single copper strand is then fixed against this head. A notch made in the head of the match keeps the strand in its place. Tape is used to fixate all the parts. The cool part of this project is that you can remotely ignite the match.

We used both two 9V alkaline block batteries in parallel (as suggested by Grant Thompson) and a 6V battery that I salvaged from an old pump. Both solutions work perfectly although with the 9V block batteries the match ignited faster. I used two alligator clips to connect the igniter to the battery. I placed the igniter is a third hand to prevent that it sets something on fire by accident.

A word of caution. The 6V battery that we used is of the sealed lead acid type. Since you will short circuit the battery it is safer to use a alkaline battery instead of rechargeable battery (lead acid, Li-ion, NimH etc). Rechargeable batteries can explode or catch fire when short circuiting it. Since I short circuited my lead acid battery no longer than a few seconds I figured that there was no danger. In conclusion it is safer to use the alkaline batteries and short circuit them only for a few seconds in a row.

So how is it possible that the match catches fire. I already mentioned that you short circuit the battery. According to Ohm’s law I = V / R. The resistance R is very low (it’s just the copper strand) while the voltage V remains the same. The current is therefore very high. The heat produced in the circuit is proportional to I2 * R * t. With the current squared the heat rapidly increased with increasing current (even though the resistance is low). At a certain point the heat ignites the head of the match.

We used these simple tools and materials to make the igniters.
The fruits of hard labour.
Make sure the strand of copper fits into the notch of the matches head.

Building a robot cart (Experiment 32 of Make:Electronics)

This experiment is about building a little robot cart. Make:Electronics describes all the steps that needs to be taken in great detail beginning with the cart and then the circuit. This experiment is a lot of work but I think it is worth it because you make a complete robot from the bottom up. The cart is much smaller than I initially thought and making small things brings their own set of problems in terms of precision and tools needed.

The cart needs a motor and I salvaged one from an old RC car that was lying around in the house. For this project I use a 6V DPDT relay. I decided to make the circuit first. I had some problems with the relay because the switch is connected differently than the one used in the book. Luckily this was easily solved by looking at the datasheet of the relay. I tested the motor on the circuit and it worked well.

The cart made out of plywood with a motor that I salvaged from a old RC car. I grinded away some unnecessary parts of the housing of the motor. 

Next I created the cart. I made the cart of 1/4″ thick plywood and not the ABS material that is suggested in Make:Electronics since I have no experience with ABS. I cut the plywood and connected the pieces with screws and bolts and nuts for the wheels. The cart looks pretty good (I think) and maybe a good platform for further experiments. There are two potential problems with the cart. First the wooden wheels lack grip. Maybe I’ll cover the surface of the wheel with rubber tape to overcome this. Second the motor is spinning fast maybe too fast for the cart. The cart might crash because of this. This could be solved by adding some gears to the motor but that would complicate things. For now I will just wait and see what happens once the cart is finished.

Next I will solder the circuit on a piece of perfboard and fit it on the cart. The book describes the principle of limit switches to create a better steering mechanism (p278). The author doesn’t describe in detail how to add this to the robot cart but I might be a nice addition to this experiment.

Circuit of the robot cart with a 555 timer triggering the relay. The motor is reversed when the relay is energised. The LED indicates that the 555 timer is triggered (by the switch). With the trimmer sets the length of the 555 pulse The pin lay-out of the relay is different from the ones described in Make:Electronics (p58).
Overview of the cart. The hinged trailing wheel is not yet connected to the cart.

Homemade camera dolly

Finished camera dolly made out of Makeblock and plywood. The plywood is painted black with a regular (alkyd) spray paint.

I make a lot of video’s of our projects so I figured a camera dolly would be a nice addition. I could buy one of course but making one is a lot more fun. About a year ago I bought a Makeblock starter robot kit. The supplier that I bought it from was offering it with a nice discount at the time. The purpose of Makeblock is prototyping but I never used it, until now. Makeblock offers a versatile, sturdy and extensible platform for the camera that seemed very suitable for this project. Even better an Arduino Leonardo clone is included so programming it is not too difficult.

Makeblock claims they have an open source hardware and software platform. Makeblock uses an Arduino clone, called Baseshield, and Arduino is truly open source software platform. The Baseshield uses the RJ25 a 6 pin connector (known for their use in telephone lines) to interface with their sensors. Although this RJ25 is easy to use it is not so easy to connect a generic electronic component to it. This can be avoided by just replacing the  Baseshield with a regular Arduino (EDIT: something I haven’t done in this project). Furthermore Makeblock provides free downloadable CAD drawings of their mechanical parts such as the beams and gears.

I found an example of a Makeblock camera dolly in the internet but unfortunately no documentation was provided. I therfore had to improvise using the Makeblock components that I had. My Makeblock dolly also has four wheels and only a couple of beams are needed. It is very sturdy. It uses two 6V motors that came with the starter set. Each engine has a simple transmission to a wheel via a belt and a couple of gears. The combination of the gears reduces the speed of the motor.

I needed a solution to attach the camera to the Makeblock beams. I decided to make a plywood frame for the camera since I have a lot of plywood lying around. Plywood is cheap but strong enough for this application. With this plywood frame the camera is able to tilt up and down and rotate. With the bolt and nuts I can fix the camera in a desired position.

The plywood frame that serves as a mount for my Xacti camera. The frame is made out of 1/2″ thick plywood cut in strips of 1-1/4″ width. The frame is assembled with 1/4″ bolds and nuts.

The camera mounted on the frame. 

I had to place the camera a bit outside the frame to be able to open the display.

I could have used any other material to make a camera dolly than Makeblock but that would probably have taken considerably more time. On the other hand using wood or plastic is much cheaper. The aluminium mechanical parts are fairly expensive. Some Makeblock parts can easily be replaced by cheaper alternatives. For instance all screw are 4 mm screws which can be bought at the local hardware store. Same goes for shafts and nuts.

The dolly in action with the still unpainted frame.

All in all I’m happy with the result although the dolly still needs some work. First the dolly has a slight tendency to move to the left. I exchanged motors, gears and wheels from left to right but that didn’t made a difference. Also the dolly has no suspension at all which can lead to unstable video’s.

I added a YouTube video below to demonstrate the camera dolly.

Breadboard malfunction (redo experiment 29 and 30 of Make:Electronics)

During experiment 29 and 30 of Make:Electronics I noticed that the circuit were very susceptible to noise to the point that it really interfered with the experiments. While thinking about it I suspected that something was wrong with the breadboard. I decided to redo both experiments with a another breadboard (but without the low pass and high pass filter). I immediately discovered that the sound was more clear than before. I also discovered that at 9V the circuit only took 40mV whereas the same circuit on the old breadboard took 200mV. A clear sign that the old breadboard was malfunctioning (possibly due to a burn-out).

Previously I wrote about the TEA2025B amplifier becoming very hot. So hot that I decided to reduce the voltage of the circuit from 9V to 4.5V. The same amplifier in the current breadboard is not hot at all even at 9V! Not surprisingly since the heat generated by the amplifier is proportional to the square amperage.

The lesson here that when that even the unsuspected elements can be a variable in experiments.

Redoing experiment 29 and 30 on another breadboard was worth. At 8,9V the circuit only needs 40mA. Not only did I get rid of all the noise also the circuit needed only one fifth of the amperage. Visible on this image is part 2 of experiment 29.
Closer look at the breadboard with on the left the 555 chip with a black and blue trimmer surrounding it. On the right the TEA2025B amplifier. The circuit on the breadboard is same as the shown in figure 5-41 of the book without the low and high pass filter. 

Fuzz: experiment 30 of Make:Electronics

After some refurbishing around the house I’m finally back with Make:Electronics. In experiment 30 I used most of the circuitry from experiment 29. The idea is to create a distorted sound. The base of an NPN transitor receives the output from the 555 timer thus controlling the base of another NPN transistor (see fig 5-55 of the book). The base (not the emitter since amplification is not needed) of this second transistor controls the amplifier (TEA2025B). The input of the amplifier is overloaded thereby creating a distorted sound (fuzz)

Building the circuit is easy enough since I could use most of the circuit from experiment 29. The most important change, besides some resistors and capacitors, is the addition of two 2N2222 transistors. For the output adjustment of the transistors I used a 50K potentiometer instead of a 100K. Trouble began when I tested the circuit. Amplification of the audio input worked fine (although the circuit is susceptible to noise) however I couldn’t get the distortion to work. I determined that the 555 chip was working fine but couldn’t get a signal on the base of the first transistor. I switched the two transistors with each other to no avail (these are the last in my stock).

When I came back to the circuit a little later I noticed that the voltage was very low (about 5V). I had done that on purpose when I initially tested the circuit not wanting to overheat the amplifier but I hadn’t increased it afterwards. I increased the voltage to the required 9V and suddenly I had a beautiful harsh distortion coming out of my speaker (which annoyed my oldest son slightly since he was doing homework on the same floor). Next I’ll play around with some capacitors and resistors to change the distortion effect.

Overview of breadboard with 555 chip on the left and the amplifier on the right. In between them two 2N2222 transistors creating a distorted sound. The wires to the right are connected to the speaker and wires to the top provide audio input. Not captured is the 50K potentiometer (connected to the alligator clips). It adjusts the output of the transistors.
A closer look at the two transistors. At the top is the audio input visible.

Audio filtering, experiment 29 of Make: Electronics part 4 (finished)

I finally reached the second stage of Experiment 29 of Make: Electronics. In the first stage I used an audio amplifier (TEA2025B) and a coil to create a crossover network. During this first stage the source of the audio was an iPod (read here). In the second stage the iPod was replaced by a 555 timer as described by figure 5-51 of the book. In the astable mode the 555 timer generates a square wave. This square wave is led to the audio amplifier. A 100K trimmer between pin 6 and 7 is used to change the frequency of the square wave. The output of the 555 chip (pin 3) has, besides a 680K resistor, a trimmer connected to it. This trimmer is to be used to control the volume.

Circuit used for this experiment. The cardboard box proved to be a good box for this experiment. It has a 4-inch speaker built-in. Just in front of the soldering iron is the coil creating a low pass filter.

Contrary to the book I used a 220 ohms resistor on pin 3 instead of the 500 ohms (which I didn’t have). Because of the problems with the high temperature of the TEA2025B (read here) I used a voltage of 7V instead of 9V. The circuit is functioning great and with the 100K trimmer I was able to change the pitch. The square wave that is generated makes a harsh somewhat unpleasant sound.

The final part of this experiment the low pass filter and the high pass filter will be used (again). I will describe that in my next post but that won’t be until the end of July. Today my summer holiday has started and I will be gone for a couple of weeks.

UPDATE: I used the low and high pass filter. Not surprisingly the low pitched sound generated by the 555 chip is passed on much better by the the low pass filter while the high pass filter generates hardly any sound at all. Reversely the high pitched sound is passed on by the high pass filter while it is hardly audible through the low pass filter.

This concludes experiment 29. In experiment 30 this circuit is used once more to demonstrate and audio distortion.

A closer look at the breadboard with on the far left the 100K trimmer. Next to it the 555 timer in astable mode. In the middle the TEA2025B amplifier and on the right the blue 220 ohm trimmer.

Audio filtering, experiment 29 of Make: Electronics part 3

A small update on the filtering experiment 29 of Make: Electronics that I wrote about earlier this week. To improve audibility especially of the lower frequencies I had to built an enclosure. The book proposes a plastic box but I had a shoebox made out of cardboard lying around. I cut a circular hole in it just wide enough to fit the 4-inch speaker and fastened it with four bolts and nuts. I placed the breadboard with the amplifier on the bottom of the shoebox. I connected the audio and power and filled the box with isolating material. Then I played a track unfiltered, with low pass filter and with high pass filter. The box definitely made an big improvement to the sound. Conclusion: a shoebox can make a tolerable (and cheap) enclosure for a speaker.

Cardboard box with speaker built in. Labbench and iPod for power and audio-in respectively. 

Breadboard on the bottom of the shoebox with the coil clearly visible. The coil acts as a low pass filter.

Shoebox stuffed with isolating material in an attempt to improve the sound for this experiment.

Audio filtering, experiment 29 of Make: Electronics part 2

Finally, after earlier setback, I’ve got the amplifier and 4-inch speaker working properly. I tried multiple setups today and managed to get rid of the distortion. The book dictates 9V, 33K resistance on audio input. This results in my case in a temperature of 90 degrees (194 fahrenheit). Which is uncomfortably high. I therefore decreased the voltage to 6V DC, increased the audio input resistance to 100K and added 10 ohm resistance to audio output. This gave a workable temperature of 60 degrees (140 fahrenheit). Because of these high temperature it is likely that the TEA2025B amplifiers that I bought for this experiment are part of a rejected batch.

After having solved this problem I added the coil, as a low pass filter, and the 11 uF bipolar capacitor as a high pass filter. Both filters work great with low frequencies on the low pass filter and high frequencies on the high pass filter. The coil is the same that I used in experiment 28 and the bipolar capacitor was made of two 22uF electrolytic capacitors.

Next I’ll fit the speaker in a shoebox and create a waveform with a 555 chip as an input for the audio amplifier (instead of the ipod).

Overview over the experiment with on the left the power supply, in the middle the ipod and on the right the breadboard.

A top-down view of the 4-inch speaker (top), breadboard and coil (bottom)

Close-up of the breadboard with on the left the TEA2025B amplifier. 

Audio filtering, experiment 29 of Make: Electronics part 1

This experiment of Make: Electronics demonstrates the use of self-inductance and capacitance in audio filtering. The low and high frequencies of the audio signal can be separated and send to different speakers (woofer and tweeter). The audio chip used for this experiment is the TEA2025B, a somewhat older chip that was used in portable radio cassette players (remember the Sony Walkman). For this experiment I needed a 5-inch speaker. I was able to find an old woofer that came from an sound system that’s no longer in use. This particular woofer is 4 inch , 6 ohm (according to the book a minimum 5-inch and 8 ohm speaker is required) and maximum of 40W. I made the two nonpolarized capacitors out of two 220uF capacitors as indicated in figure 5-38 of the book (pg. 249). The experiment requires two .15uF electrolytic capacitors which I do not have. I use two 100nF ceramic capacitors instead.

I have build the circuit temporarily without filtering for two reasons. The first reason is that I want to use this circuit to test the TEA2025B’s that I bought from Aliexpress which were in a very bad shape when they arrived. Secondly I want to rule out problems in the non-filtering part of the circuit.

Overview of the experiment. With on the left side the 4-inch speaker. The audio is supplied by a Nexus 7 inch tablet.

My first try didn’t go so well. After powering up the circuit the first half minute or so the sound is sort of ok but than a terrible distortion kicks in and makes listening unbearable. Furthermore the TEA2025B becomes extremely hot. I unplugged and checked for errors but couldn’t find none. I figured that I’m overdriving the amplifier so I increased the 33K and 10K resistor to 100K and 33K respectively without result. I then changed the TEA2025B for another one, again no result. Finally I decreased the voltage to 4,5V (instead of 9V). Now the distortion is gone but I’m still not happy with the sound quality. The sound is very muffled and undefined (sorry I don’t have any words to describe it). Not sure how to go forward from here.

Close-up of the breadboard. The oddly shaped capacitors are the non-polarized capacitors that I made from 220uF capacitors.

Making a Darth Vader voice changer, part 3

I finally finished the Darth Vader voice changer this weekend. I took a belt with two snap hooks from an old bag. Next I fitted the box with the voice changer with two black screw eyes that were large enough for the snap hooks. The enclosure is now comfortable around the neck of a child. In a local electronics shop I bought a case for a 9V battery that fitted nicely in the box. Finally I taped the mic into the Darth Vader mask and the fun could begin.

My two boys both volunteered and got dressed as Darth Vader.  We still have a dark cloak that goes well with the mask. Unfortunately we sold the lightsabers a couple of years ago. The Darth Vader voice is surprisingly convincing but only if you play around with the settings. Even funnier, you can make Darth Vader sound like a robot or as someone that has just inhaled helium (a very high pitched voice). I can imagine children having a lot of fun with the voice changer at a party or at Halloween.

Is there something left to be desired? Yes, the voice changer has four buttons for robot voice, vibrato, higher or lower pitch. As mentioned before I somehow couldn’t get the external red push buttons functioning that were placed on the enclosure. So I used the pushbuttons on the MK171 board instead. To access the four pushbuttons on the MK171 board I need to open the enclosure. This is far from ideal and something that needs to be fixed in my next version of the voice changer.

Darth Vader complete with mask and cloak. Unfortunately the lightsaber is missing.

A Belt with two snap hooks, screw eyes and battery holder for a 9V battery complete the Darth Vader voice changer.

Enclosure, now with screw eyes.

Inside of the enclosure with battery holder.