Last weekend I had a chance to continue with the next experiment. Make:Electronics suggests to set it up on the same breadboard that still has experiment 16 on it. This is for later experiments when the 555 timers will be chained. Again this is an easy experiment although I almost forgot all important connection between pin 6 (threshold) to pin 2 (trigger). Instead of one pulse in the monostable mode a stream of pulses is generated. The loudspeaker that is connected to the pin 3 (output) generates a (faint) tone. According to the book it is 1,5KHz (this equals to 1500 pulses per second).
This experiment (and the next experiments) are centered around the 555 timer chip. The circuit that been built (figure 4.14 of Make:Electronics) results in the monostable mode of the 555 chip. Once triggered the 555 emits a single pulse of a fixed duration. I lacked the required 5K linear potentiometer and I used a 2.5K instead. I decreased the resistance of the potentiometer step by step and at a certain threshold the led that is connected to the pin 3 (output) emitted a pulse. At this time I measured a voltage on pin 2 (trigger) of 3V. This experiment is straightforward and I encountered no problem. Afterwards I changed the capacitor on pin 6 (the threshold pin) from 47uF to 22uF. The duration of the pulse halved as expected.
I spent several hours fault tracing the circuit from the intrusion alarm. I used the multimeter together with the minigrabber and checked the relay part of the circuit. I was able to measure the voltage over all the components and at first couldn’t find any problem. I decided to replace the transistor since the soldering looked a bit messy. Tried it again and nothing. Then I started applying power directly different parts of the relay circuit. I found that the first resistor (the 10K resistor in figure 3-93 of the book) had a bad connection and blocked the current. The solder joint looked messy. I cleaned it using a solder-pump and soldered it again. Problem solved.
Next I wired the external parts to the circuit board. I finished the soldering and then powered the circuit and again no click in the relay and no alarm. The led’s in the enclosure worked fine however. I took out the circuit and tested it. It works without a problem. So I’m clueless.
Nevertheless I learned a lot from this chapter and especially experiment 15. I learned to make simple circuits and mount everything in a box although I can certainly improve my skills on this. For the moment I will leave the intrusion alarm (it’s taken far too long for my taste) and continue to the next chapter (chips). Maybe I will revisit the intrusion alarm later.
I completed the projectbox yesterday. It is looking good (well good enough) and I was eager to wrap-up the project. Just a few solder joints and it was finished. Before I started soldering, as I final test, I screwed the circuit board in the box and plugged in the power, I opened the magnetic sensor and… nothing happened, at least no audible sound either from the relay or the loudspeaker. I checked the voltage on the noise making part of the circuit, nothing. Then I checked the relay part. I measured voltage but the relay will not energize. Probably something has happened when I screwed the circuit board. Now I’m stuck with a nearly finished projectbox and an apparently broken circuit.
When frustration builds up I have learned to leave a project alone. You might end up throwing the project out of the window. On the up-side this may be a learning opportunity. On page 139 of Make:Electronics is an explanation how to trace faults in a circuit. I had no need for that until now. It is also an opportunity to use the minigrabber (see Figure 3-6 of the book) that I had recently bought.
I solved the problem with the circuit. I simply forgot to place a single wire that powers the coil. After this I was ready to solder the complete circuit on the Adafruit perfboard. I started with the noise making part of the circuit and tested it. Then I continued with the sensor and the relay part. It’s strangely exciting to power the board for the first time and hope it works fine. In my case it did so no frustrating fault tracing although one can learn a lot from this. I’m happy with the result but I now need some components before I’m able to finish experiment 15. This experiment includes placing the soldered board in a project box and add some user control to the intrusion alarm.
|Completed circuit on the perfboard.
|Overview of the perfboard, magnetic sensor and loudspeaker.
I had to scale down the circuit that I had built before because the perf board that I’m going to use is pretty small (Adafruit Perma-Proto 1/2 Sized Breadboard). I also decided to change the relay that I used for another type. I previously used the SRC-S-12VDC which works fine but the pin layout is different from the relay used in Make:Electronics. So I used the FTR-F1 CD 012 which is one of the recommended relays in the book. Once I built the circuit everything worked fine except for one thing. Once the alarm is triggered by the magnetic sensor the alarm should be locked even if the magnetic sensor is closed again. This is not the case. I went over the circuit several times but I couldn’t fix the problem. I don’t want to waste to much time on this so I think I will build the alarm without the lock.
A couple of years ago I started working with electronics as a hobby. The reason was that it seemed cool to create electronics gadgets and learn about electronics in the process. I had limited training in electronics so I decided to start with simple electronics kits. These kits contain a PCB, electronic components and a simple step by step instruction. So I built a FM radio, an amplifier and some simple LED gadgets but apart from enhancing my soldering skills I didn’t learn much about electronics. Then at www.makezine.com I came across the Make:Electronics book by Charles Platt. The book from 2009 but it looked very hands-on and I ordered it. By now I have almost finished the first three chapter and I arrived at experiment 15 which proved to be the most challenging so far.
In experiment 15 I have to build a alarm circuit. After some setbacks I have a working circuit on breadboard.
If you’re interested here is a link to the next part of this experiment: https://homehack.nl/building-an-intrusion-alarm-part-2/