electronics Make:Electronics

Make: Electronics Experiment 25

I skipped experiment 24 of Make: Electronics. The reason is that I’m not really interested (at least not right now) in completing the Intrusion Alarm. I do appreciate what the author of the book, Charles Platt, is trying to achieve. He gives a couple of good hints for upgrades of the Alarm without presenting the complete schematics for the upgrades and leaves it to the reader to finish the job. However, I have yet got to find someone who did finish experiment 24. Anyway, I’ll move to the last chapter of the book. In chapter 5 the topics branch out. Since I’m mostly interested in audio electronics I’ll continue with experiment 25 to 30. These experiments cover magnetism, speakers and audio filtering.

Experiment 29 and 30 require the TEA2025B audio amplifier from STMicroelectronics. This IC is very hard to acquire locally. I finally ordered 50! of them in China ( for a very low price (14 cents a piece). Until I receive them I continue with the other experiments.

Experiment 25 demonstrates magnetism as an induced effect of electrical current through a wire. A long piece of wire is winded around the shaft of a screwdriver. The ends of the wire are connected to an AA battery (see image below). Due to the induced magnetism a paperclip or some other lightweight iron is attracted to the screwdriver. Very neat. This experiment in one form or the other can be found numerous times on the web. A nice example is Colin Cunninghams YouTube movie on the subject at

Experiment 25: Wire winded around the shaft of a screwdriver.

Tada, magnetism induced. I used eight feet of wire and a 9V block battery.

electronics Make:Electronics

Make: Electronics Experiment 23 part 2

In this part of experiment 23 of Make: Electronics the binary counter from part 1 is upgraded to a dice simulator (figure 4-109 on page 219). A 74LS27 chip is added. This chip has three NOR gates of which one is used for this experiment. Also an LED display is added. The configuration of this display represents a die. The speed of the 555 chip is changed from 1 to 50.000 pulses per second. When the pushbutton is released the new 68uF capacitor discharges over the 555 chip and the frequency of this timer will slowly decrease and eventually forcing the LED display to stop at a number between one and six.

For this experiment you need to take extra care because of the complexity. First I made a mistake with the addition of the (68uF) capacitor and the push button. I had placed the push button in one vertical row on the breadboard and effectively shorting it (I know that’s stupid). Luckily I noticed that the LM7805 voltage regulator was becoming very hot. Furthermore it also took me some time to figure out a good configuration of the LED display. After this I encountered no further problems. I tested the circuit and found out that it appears to be randomly ‘throwing the die’. After 30 ‘throws’ all numbers from one to six appeared exactly five times.

I do not have the 74LS06 chip that is needed for the enhancements paragraph (page 220) of this experiment so I will skip that.

I uploaded a video of this experiment on YouTube at

Overview of experiment 23. On the left side is the LED display representing a die. In the middle the 74LS27 is added. On the right a 68uF capacitor and a push button are added. Also note that the configuration of the 555 chip is added (instead of one puls per second it generates 50.000 pulses per second).

electronics Make:Electronics

Make: Electronics Experiment 23 part 1

Experiment 23 of Make: Electronics uses 74LSxx chips (TTL chips) instead of the 74HCxx (CMOS) that has been used in previous experiments. In the first part of this experiment a simple binary counter in made (figure 4-102). I ordered some low current LED’s especially for this experiment to be able to see the output of the circuit. The circuit, with three binary output pins connected to a LED, can count from 0 (000) to 5 (101).

I encountered no problems building the circuit and with the low current LED the output was clearly visible. The only detail that puzzles me is that the 74LS92 counter has a Clock input B (pin 1) and Clock input A (pin 14). The output from the 555 chip (pin 3) is connected to Clock input A nevertheless Clock input B needs to be connected to Binary output A (pin 12) of the 74LS92 counter. Anyway everything works fine.

At the bottom of this post you’ll find a video of me explaining the experiment.

Breadboard with the binary counter. The 74LS92 counter (left) is triggered once every second by the 555 chip. The three LED on the left indicated the output from the counter.
electronics Make:Electronics

Make: Electronics Experiment 22

Experiment 22 of the book Make: Electronics is a simple experiment to demonstrate use the 74HC02 logic chip as a flip-flop. The 74HC02 is a logic chip with four NOR gates. The schematic of this experiment can be found in figure 4-98 on page 21 of the book. A SPDT switch is used to flip the circuit in one of the two possible states. The state is indicated by two LED’s connected to two different NOR gates. Other input, in this case pulling a wire from the switch out of the breadboard, is ignored by the circuit (debounce).

Building this circuit is simple by now. I already soldered wires to the SPDT switch for the previous experiment. When the circuit is powered one of the LED’s lights up. Flipping the switch lights the other LED. When I turn the switch a positive current is send to the a NOR gate. The negative current of this NOR gate crosses over to the input of the other NOR gate creating a positive output on this gate. The circuit can be rewired with NAND gates (74HC00 logic chip) and negative switched input.

A video of this experiment can be found on my YouTube channel at

Breadboard with simple flip-flop circuit based on the 74HC02 logic chip. 

Close-up of the flip-flop with two LED’s green and orange, indicating the state of the circuit. A connection between pin 3 and 4 is invisible on this image due to the (green) connection between pin 1 and pin 6 above it. These connections function as cross overs between the two NOR gates.

electronics Make:Electronics

Make: Electronics Experiment 21

Experiment 21: Race to Place from Make: Electronics describes a circuit useful for a quiz show like Jeopardy. Pushing a button lights an LED and locks the button of the other player(s). The two player schematic is depicted in figure 4-95 on page 208 of the book and is built around the 74HC32 logic chip (with four OR gates) and two 555 timer chip in bistable mode. The circuit can easily be extended to three players (figure 4-94). Pushing a button (e.g. S2) triggers pin 2 of the first 555 timer. The output from this timer locks pin 2 from the other timer by keeping the voltage high.

Compared to the previous experiment this circuit is relatively easy to build on the breadboard. Nevertheless, I made a mistake. I forgot to connect the output of the second OR gate of the 74HC32 chip to the second 555 timer. As a consequence pushing S3 didn’t light up the second LED and the other button was not locked.  After comparing the circuit on the breadboard with the schematic I discovered my mistake and corrected it.

I uploaded a video on this experiment to my YouTube channel at

Close-up of the circuit on the breadboard.

Overview of the circuit with the two tactile switches, S2 and S3 and the SPDT switch S1.

electronics Make:Electronics

Experiment 20: A Powerful Combination part 2

After having done most of the circuitry of Experiment 20 yesterday today I connected the relay and all loose wires from the keypad to the circuit. I had to read the description of some of the experiments with relays earlier in the book Make: Electronics (e.g. experiment 7) again to be able to wire the relay correctly. I added a yellow LED indicating that the relay is flipped in the off state and a green LED relay indicating that the relay is flipped to the on state (see image below).

The circuit now functions as follows. When the asterix is pressed the LED on the right side of the circuit is lit. While this key is pressed the code 1-4-7 is pressed. Next the LED just above the 555 is lit for a brief moment. Then the relay flips on and the green LED lights up. To flip it off again I have to press the hashtag on the keypad, the relay flips off and the yellow LED lights up.

I noticed on YouTube ( at 2:30) that another reader of the book needed a 2N2222 transistor to amplify to signal from the 555 timer. I had no such problem.

I made a short video of this experiment. You can find it on YouTube at:

The yellow arrows indicate the wires from the hashtag on the keypad and the output of the 555 timer to the relay.

The yellow arrow on the left indicates all other wires from the keypad (0,2,3,5,6,8,9) to the first inverter on the 74HC04. The other yellow arrow indicates the LED that is lit after the asterix is pressed on the keypad.

electronics Make:Electronics

Experiment 20: A Powerful Combination part 1

Experiment 20 of Make:Electronics describes a hardware device that protects a computer (or any other electrical device) from being used unless a specific numeric code is entered on a keypad. The experiment is built around two 7400 logic chips (74HC08 and 74HC04). These chips process the input from the keyboard and trigger a 555 chip if the three digit input is correct. The 555 chip in turn switches a (latching) relay.

Initially I had a problem finding a numeric keypad suitable for this experiment. The Velleman 12 keys Keypad KP-12 wasn’t available at my local supplier. Luckily I found an alternative that is fulfilled the requirements (and looks suspiciously similar to the Velleman).

Breadboarding was done according to figure 4-84 of the book. I double checked all the connections. At this stage I left the relay out and tested the circuit. After punching 1-4-7 the LED on the output the 555 timer lit up however with further testing I discovered a problem. Every numeral code that includes 1 and then 7 lit up the LED (e.g. 1-9-7). After comparing the circuit on my breadboard with figure 4-84 I discovered that I mistakenly had pin 4 and pin 5 of the 74HC08 logic chip connected (see image below). Also digit 4 of the keypad was connected to pin 5 instead of 4. After I corrected the mistakes everything worked fine. Next I’ll try to connect the relay to the circuit.

Overview of the circuit on the breadboard. Relay is disconnected from the rest of the circuit.

The mistake that I made visible in the ‘fish eye’

electronics Make:Electronics

Make:Electronics, Experiment 19: Learning Logic

With experiment 19 of Make:Electronics I’m entering the world of pure digital electronics. This experiment explains the basics of the 7400 family chips. It is also a prelude to experiment 20. First an LM7805 voltage regulator is used to to provide precisely 5 volts DC. Then a simple circuit is built around the 74HC00 chip (the NAND chip of the 7400 family). This circuit (figure 4-46 of the book), shown on the image of the breadboard below, demonstrates the function of one NAND gate (out of four on the chip). Two tactile switches provide input on the NAND gate and the LED provides a visible output. As expected the the LED lights up if none or one tactile switch is pushed. If both tactile switches are pushed the light of the LED goes out.

Next I replaced the 74HC00 with the 74HC08 chip, which is the AND chip. This chip functions opposite to the NAND chip. So only when I push the two tactile switches simultaneously the LED lights up.

In the last part of this experiment a diode is introduced. It connects the output of the first AND gate with an input of the same gate (figure 4-79 of the book). There is only one tactile switch left since the first pin is connected directly to the positive voltage. Once the tactile switch is pushed the LED lights up and stays on even if the switch is let go (like a latch).

Overview of experiment 19 with the LM7805 on the right. 

With 74HC00 NAND chip.

Latch configuration with pin 1 connected to positive voltage and a diode connects pin 3 to pin 2.
electronics Make:Electronics

Experiment 17: Set Tour Tone revisited

While working on the Atari Punk Console I reread the part of chaining chips in Experiment 17 of Make:Electronics (pg167). I then realized that I didn’t do all the experiments that are described in the book. Since Experiment 17 contains a lot of information and chaining 555 chips is common practice in electronics I decided to at least one of the remaining experiments. This experiment is described in figure 4-30 (pg169). In this experiment the output of the first 555 chip is connected to the control (pin 5) of the second 555 chip. Both timers are in astable mode. The second chip drives a speaker. The first 555 chip, that oscillates slowly, slowly decreasing the pitch of the of the sound generated by the second chip until the cycle of the first chip ends and the frequency drops. This results in a slow whoop like the sound of a siren.

After building the circuit the sound produced was very distorted and unlike the slow whoop I was expecting. The LED connected to the first chip performed as expected with about one pulse per second. After inspection of the circuit I noticed that the 100 ohms resistor in series with the speaker had become very hot. I changed it for a resistor of 180 ohms and now the circuit worked fine. I substituted a 10K potentiometer (see images below) for the R7 resistor (1K) which made some interesting changes in the slow whoop (higher or lower pitched).

At this point in the book I believe the use of an oscilloscope would become interesting even helpful.  I would be able to analyze the waveform on several pins of the circuit. The oscilloscope is however an expensive piece of equipment which I don’t own yet. It will put it on my wish list. Something I noticed with this hobby that there appears to be an ever increasing need for space, equipment and components.

I’ve added a video of the experiment, with several tweaks of the circuit,you can watch it at the bottom of this page.

Complete circuit of figure 4-30. R7 is substituted with a 10K trimmer.
Close-up of the circuit.
electronics Make:Electronics

Experiment 18: Reaction timer part 5 (finished)

I (almost) finished the reaction timer today. That means that the delay is build in. This was done by adding yet another 555 timer now in monostable mode. It is triggered with a tactile switch connected to pin 2 of the timer (see pg. 178 of Make:Electronics). During testing of the circuit the LED switched on immediately which was not supposed to happen. After some investigation I discovered that the resistor connected to pin 7 of the last added 555 chip was 330 ohm instead of 330k allowing the capacitor (C5) to be charged far to quick. After solving the problem I exchanged the capacitor of the first 555 chip (C2 in astable mode) from 100uF to 0.1uF increasing the number of pulses per second a thousand fold. Finally I was able to test my reaction. In conclusion Experiment 18 is by far the most complex circuit that I plugged into a breadboard. Nevertheless due to the step-by-step of the book approach I was able to complete without too much trouble. Linking IC’s together is demonstrated very well with this experiment.

Further text at page 179 and 180 suggests how to calibrate the whole circuit without an oscilloscope. At this point I’m not sure if I want to do this because I don’t want to take this project any further by enhancing it or even create a project box.

The video of the different stages of experiment 18:

Summery video of all the stages of experiment 18
Overview of the finished circuit.
Close-up of the three 555 chips in the middle with on the left the 555 timer that provides the delay.