Category: electronics

The next step in Experiment 18 of Make:Electronics is the addition of a 555 timer in astable mode to the circuit (pg. 175 of the book). This addition drives the decade counter therefore the tactile switch that was connected to pin 1 of the first decade counter from the previous part of the experiment had to be removed. At first I had the two capacitor exchanged so instead of four pulses per second the display counted frantically. After solving this I encountered no further problem. For the larger capacitor connected to pin 6 of the 555 chip I used 100uF instead of the 68uF so my circuit is probably down to three pulses per second.

Circuit with the 555 timer included however the two capacitors (above the 555 timer) were exchanged.

Circuit with the capacitors in the right place.

Last Friday I’ve built the circuit as displayed in figure 4-37 (pg. 174) of the book Make:Electronics. The circuit consists of (in my case) three Kingbright 7 segmented digits. Each digit was connected to a 4026 decade counter. The decade counters are coupled by connecting the output of pin 5 (carry) to the clock input (pin 1) of the next counter. These are the blue jumper wires in the middle of the images below. As you can see a lot of jumper wires were needed. Every pin of the decade counters needs to be connected either to the digits or to the positive or negative voltage.

When I applied voltage to the circuit for the first time a problem occurred. The display immediately showed random numbers although I did not touch the tactile switches. A closer examination of the circuit showed me the cause of this problem. The pull-down resistor of the push button clock input of the first counter was not properly connected. This problem was easily fixed and the circuit worked then flawlessly however with one mistake. I had connected the first decade counter to the leftmost digit instead of the rightmost.

Although this experiment is a bit tedious with all the connections it was worth the trouble once I saw that the display worked properly and I was able to count to 999.  

Overview of the circuit corresponding to figure 4-37 of the book.

Top down image of the circuit where the  tactile switch to the left is connected to pin 1 (clock input) and the switch to the right is connected to pin 2 (disable clock) of the first counter.

With the arrival of the Kingbright numeric LED with the correct width (see my earlier post) I was able to continue experiment 18 of the book Make:Electronics (pg. 170). In this experiment the reader will eventually build a reaction timer using the 555 timer chip and 4026 decade counter. The layout of my numeric LED is a little different than the one from the book so I have to change the connections to the 4026 decade counter later in the experiment accordingly.

In the first part of this experiment you simply test display. This is done by sticking the three numeric LED’s in the breadboard and applying voltage to the succesive pins. Before applying the voltage I connected pin three of every LED to the negative site with a resistor in between. Then I connected positive voltage to all the other pins (see image below).

Next I connected a 4026 chip to one numeric LED. Connecting is easy. The only problem is that I needed a lot of connections already while later in this experiment all three LED will be connected. Pressing the tactile switch sometimes prompted the display to skip a number. This effect is described as switch bounce and described on pg. 174 of the book. Apart from that the whole experiment went pretty smooth (see the video below). To be continued.

Applying positive voltage to a pin of the first numeric LED.

Numeric LED connected to the 4026 decade counter.

I wanted to continue with experiment 18 of the book Make:Electronics today but discovered that the Kingbright numeral LED’s that I received were the wrong type after all. The width of the component is to small to fit in the breadboard (it is 2/10 inch instead of 3/10 inch). I ordered the 3/10 numeral LED’s right away and decided to revisit the intrusion alarm. A couple of weeks ago I was unable to finish this project. Back then the circuit board worked fine until I connected all the external components to it (see here). I decided to build the external components on the breadboard and connect this to the circuit board. I discovered that the LED connecting the circuit board to the anode caused the problem, possibly due to the drop in voltage of the whole circuit board. Remember that the system needs 12V. If I supply it with 9V the relay refuses to switch. I decided to leave this LED out, soldered all the external components and fit everything in the project box. This time it works without a problem. To bad about the missing red LED that had to indicate that the alarm was armed. The video of the experiment can be found on YouTube.

Image of the finished Intrusion Alarm.

A small update. Saturday I received the rest of the components that I need for the Reaction Timer (Experiment 18 of Make:Electronics) and the rest of chapter 4.  I couldn’t get all the components on the shopping list (see pg. 147) from my online supplier so I had to choose some alternative components. Notably the Panasonic latching relay (I got an Omron which shouldn’t matter) and the Kingbright LED numerical display (couldn’t get the three numerals in one package so I ordered three individual numerals). Since the book only describes the three numerals in one package I had to find the pin outs of the individual numerals that I have. A simple Google search gave me the datasheet on the Kingbright USA website (here). Unfortunately I had no I time to get started with experiment 18 because I was refurbishing our bathroom this weekend (Off topic. I discovered that the Dremel is very handy while cleaning the seams between the tiles of the bathroom).

Part of the data sheet of the Kingbright SC36-11EWA (pin out at the bottom right of the image).

Kingbright SC36-11EWA numeral LED’s.

The Omron latching relay that I received.

I reread the part of Make:Electronics about the inside of the 555 timer in the astable mode (page 162 of the book) hoping that this would give me a clue about what went wrong with the Valentine LED chaser. This gave me the idea that the 1 uF capacitor connected to the pin 6 of the 555 timer wasn’t properly charging or discharging. After examining the circuit board I understood why. I had soldered the 10K resistor protecting the potentiometer to the wrong side of the capacitor, the negative side. Therefore the capacitor simply didn’t charge. I disconnected the resistor from the negative side of the capacitor and re-soldered it to the positive side. Everything worked fine now. I’m glad the circuit works however the lay-out of the circuit could have been simpler to avoid the spaghetti of wires that I ended up with. All in all a nice deviation from the book. With everything I learned this far from Make:Electronics I was able to finish the Valentine LED chaser (Remember that I had hardly any electronic skills when I started with the book). A short video of this project can be found on below.

Last Friday and Saturday I transferred the components to the perf board. I used regular perf board this time instead of the breadboard type perf board that I used for the alarm circuit. I had to make a sketch of the circuit on the perf board before I started to solder. The sketch was simply hand drawn and depicted all the components positioned on the perf board and all the solder joints. I realised this circuit needed a lot of soldering. The wire cutting and soldering indeed took a serious amount of time even more than anticipated. The end result looked like a spaghetti of wires (see image). I attached the 9V battery and… only one LED started glowing. Disconnecting and reconnecting the battery prompted other LED’s to glow but nothing like the LED chaser. I replaced the 555 timer and the 4017B counter. Same result. This leads to the assumption that the 555 timer isn’t properly triggering the counter. Alas no finished LED chaser for this Valentine but that doesn’t mean I’m not going to solve the problem. To be continued.

It is time to take a temporary departure from Make:Electronics. The question is: has all these theory and experiments from the book enabled me to finish my own project? After working with the 555 timer in astable mode last week I remembered an article about this chip that I read a year ago, the so called LED chaser. I read the article last year on the Makezine website. It’s an electronic circuit that illuminates ten LED’s in the shape of a heart (you can find the article here). With Valentine day next Saturday this could be a nice present for my wife. The circuit needs a 555 timer, a 4017B decade counter, some capacitors and resistors, a potentiometer and of course 10 red LED’s. Luckily I had all the components (I used 1.2K resistor instead of 1K and 250K potentiometer instead of 200K).  I have built the circuit on a breadboard today and it worked almost immediately. That leaves me almost a week to solder it to a board. Take me to part 2.