So, after putting it all together and trying it with success several times, we realized it was time for the ultimate test — triggering it with Robbie’s actual alarm clock. Off Robbie ran to get the clock, and a few minutes later we had an alarm going off.
But not the circuit.
Talking loudly worked. Clapping worked, very well in fact. But the alarm did not. Even when held quite close to the condenser mic.
We have not created an wake-up alarm light trigger, but instead have created “The Clapper” Everybody join me for a chorus of “Clap on! *clap* *clap* Clap off! *clap* *clap* Clap on! Clap off! The Clapper!”.
Hmm, what to do about this though. Robbie decided he could simply talk about the invention at the fair and show them that it triggered by voice, and hope that is good enough. But it is a disappointment to not have it fully function as we wanted.
No electronics project is complete without Magic Smoke!
We realized we needed to build all of our logic gates by hand (reference the last post), so we got to work creating OR and NOT gates. We double and triple-checked our circuit, held our breath, and plugged in the batteries.
MAGIC SMOKE! I don’t recall if it happened immediately, or only after we triggered the circuit, but some transistor somewhere wasn’t happy.
After frantically pulling all power to the circuit, I had the presence of mind to test each transistor’s temperature. It was a transistor on one of the NOT gates. That didn’t make much sense, since that is the one circuit I had already built successfully.
Now you have to wonder — are all the circuits fried? What does and doesn’t work? We started pulling wires so that each individual circuit was isolated from others, testing each part along the way. 556 chip is still good (yay!) OR gates working. NOT gates are wired correctly according to everything I know and am reading about on the Internet. Hmm… In the end, we concluded that it was probably just a bad transistor, and rewired everything. I also got a working circuit (a NOT?) and tried each of my transistors in turn in that circuit, to make sure that there would be no surprises from any of the rest.
After putting it all back together and plugging in the batteries, we tried again. Trigger…click….2 second pause….click. Not only that but with repeated attempts at triggering the circuit were ignored for 10 seconds, one of our design goals (and the reason for the 2nd 555 circuit and most of the logic gates).
Now that we are high on magic smoke, we are ready to complete the circuit!
One huge problem we have with Robbie’s science / invention fair project is that we are relying on RadioShack for parts. Yeah. That one store that USED to be a good supplier of electronics. Now they have a small part of one row, and a few drawers with SOME components.
Unfortunately they lack the following:
- Any logic ICs
- A useful set of assorted capacitors (the one bunch we bought was almost useless!)
- Small potentiometers
- Employees who have any knowledge of what these components are.
We can deal with large pots, and change some circuit values to work around their meager capacitor supply. But, the first one was a real problem. We needed some AND, NOT, and OR chips 74LS chips for our circuit to be successful.
Fortunately it hit me at some point that these circuits should be easy to build with simple transistors. So, I looked them up on the Internet. Oh duh — dead simple. In fact, I had accidentally built a working NOT gate using a transistor while trying some stuff out.
There is a good article on Making Logic Gates with Transistors on Squidoo, so I won’t repeat it in depth here.
For an OR gate — two transistors in parallel (collectors are tied to each other and emitters are tied to each other). If either one is “on”, voltage follows through the transistor and to the output (taken at the emitter). Makes sense.
AND gate — Two transistors in series — the emitter of one is hooked to the collector of the next one. So, BOTH have to be “ON” (with a voltage on the base), for the voltage to flow through the circuit. Output is taken from the second transistor’s emitter.
NOT gate — one transistor, and a resistor between the emitter and ground. The “output” of the circuit is taken right from the collector, which is tied to VCC. So, basically that point drops to zero when the transistor is on, since all the voltage drop is across the resistor at that point.
It was kind of fun doing this ourselves, and used less room on the breadboard too. We WERE contemplating rigging our NAND 74LS20 chip to do the NOT function, but that would’ve been a huge waste of space. And, when we found we needed OR gates instead of AND gates (we had 74LS08 AND chips), we realized that transistor-based logic was inevitable.
We have neglected to post what was up with the science fair project on a daily basis. Sorry!
I’ll try a quick summary in several posts, of some of the key things we did and learned after that last post about the 555 timer chip:
For some reason, the relay didn’t always fire. We were really confused by this, and thought there was something majorly wrong. One thing unusual that we had done was use ten 0.1uf capacitors instead of one 0.01uf capacitor. After buying some assorted capacitors at the RadioShack, we tried to consolidate down the whole circuit, and replaced the ten caps with only the one. Could this be the problem? It sure didn’t seem like it.
Here is the odd thing — whenever I was measuring voltages in the circuit while Robbie triggered it (by pulling a wire out from Vcc), it seemed to work. I wondered if my testing was influencing the circuit.
After a while, I just concluded that Robbie had some sort of “Magic Touch”. He could even get it to work sometimes when I wasn’t measuring things in the circuit with my voltmeter. Hmmm…
Suddenly when it was my turn again to try to pull the trigger wire, I accidentally bumped this wire with my hand. The circuit triggered and the relay ran. Woah. I suddenly realized that what the circuit needed was a high resistance path to ground so that that input to the circuit would drain all of its voltage when not directly connected to Vcc.
In other words, Robbie really did have the “Magic Touch”. When he pulled the wire, he was not as careful as me and was constantly bumping the wire and creating a path to ground, whereas I was very carefully pulling the wire straight up, never contacting the metal.
It’s a good thing we are talking about low current and low voltage here, eh?
One large resistor later, the circuit was triggering every time we’d pull the wire!
Robbie and I went to bed last night thinking that his first 555 timing chip circuit did not work. The relay was either not firing at all, or firing in rapid succession. I realized that we probably needed a diode in the circuit, and researching it showed this to be the case. At that point, nothing worked at all — the voltage coming into the relay’s coil was too small to trigger the relay.
Overnight, one of my online friends pointed out that the diode needed to be connected in parallel to the relay’s coil (we had it in serial), and I realized that a transistor was needed to overcome the too-small voltage problem.
We needed this circuit: http://www.kpsec.freeuk.com/components/relay.htm#protect
After adding in the transistor and putting the diode in correctly this time, it worked! After the trigger came in we heard, “click”….. (2 second pause)… “click”!
Do you notice in these last two pictures the capacitance problem we had? I thought i had the correct capacitors, but we didn’t. Luckily Robbie’s Digital recording lab had one correct capacitor, and 10(!) other capacitors in series gave us the value we needed for the “control voltage” capacitance on the 555(really 556) chip.
Robbie has completed the first part of his project — wiring up a K’NEX motor so that there are wires sticking out that will work as a switch. Then that is mounted to a light switch face-plate. (with holes drilled at a 45 degree angle in the bottom of the faceplate). We verified that the motor was strong enough to turn on the light switch like this, and that it took about 2 seconds to rotate one full rotation.
Next we found a circuit on the web (listed in the first entry about this), that showed how to use a 555 chip to create a 2 second signal whenever it gets a small signal as an input. ( http://www.ecelab.com/circuit-monostable-555.htm ) Robbie’s is very similar but with one more 555 chip circuit added in to make sure that the signal only comes out one time for every 20 or so beeps of his alarm. I had to teach him about logic gates to design this. Luckily we had an AND and a NAND gate chip, since RadioShack does not carry any of those.
Hopefully tomorrow he can put together this part of the circuit. Then the only thing left is the sound detection circuit. We have a few different examples of those on the Internet. One with 3 transistors, and the other with an op-amp. The op-amp uses the lowest amount of battery power, but I’m not sure how well you can adjust the noise sensitivity. He will probably just have to build it and see.
Robbie has a science / invention fair on the 17th and 18th of March (2010). He has been coming up with a whole bunch of ideas, and finally settled on one — a gadget that turns on his light in his room when his alarm goes off. With this, he will be more likely to get up and not just go back to bed.
Now we are poring over schematics for a whole bunch of circuits — sound detection — signal latching — servo or motor control. We’re pondering a whole bunch of electronics questions — is a 2N3904 transistor close enough to a BC548B to work in his circuit? If not, how does one modify the circuit to make it fit? (Radio Shack only had one type of amplifying transistor — NPN or PNP, I do not recall which). How do you interpret the markings on a capacitor?
Putting it all together will be fun too.
Yesterday being Thanksgiving, we didn’t get much design done. I mostly just got the kids thinking about the types of robots they can build — flying, bipedal, wheeled, etc. Entertaining, useful, talking, etc. The one thing that kept coming up was that they want a robot that will clean their rooms for them. Hahaha, fat chance. Actually, Helen wants one that will blow-dry her hair for her too.
So, today I floated the idea of building a dog-like robot, and the kids really like this idea. Mike has a kit we might be able to use as a base.
Here are the dog-like characteristics it will have:
- Wag Tail
- Roll Over
- Chase cats
- Play Music
- Dance to Music
- Play 20 questions
- Give you the weather
- Locate the nearest Restaurant/movie theater/etc
- It will have an “UP” dog collar with volume control
- Its feet will rotate into a position where it has wheels facing downward to travel quickly
- Shock (in alarm mode)
- Give other information(wifi connection to internet)
My friends hold a twice-a-month board game night, and this time I was actually able to go. (Usually Tara has school that night and time).
Lars invited a coworker of his, Mike, to join. As I was telling Lars about our Robot-in-two-weeks challenge, Mike mentioned that he has built a few robots! (Yay, somebody that actually knows what they are doing). He is going to loan me a book on the subject, and possibly sell some robotics electronics he does not need.
Ok, having a 7-year old tinkerer doesn’t work too well when you are in “research and design” mode(AKA watching videos on hackaday.com).
“Dad, can we please stop watching videos and go play in the leaves?”
But eventually the other to were excited by all of the possibilities and Robbie had sketched me a few drawings of what he wants (hint: everything cool, like cameras, sensors, shockers, touch-pad LCD displays, etc). Korinne created an OpenOffice drawing of a robot.
So, we have a few good ideas, but nothing concrete yet. We spent about 2 to 3 hours working on this.