thebfr.com

Make Electronics Experiment 20 – logic chip power lock

TheBFR — Tue, 09 Mar 2010 04:39:30 +0000

Experiment 20 makes use of a 74HC08 AND gate, 74HC04 inverter (NOT gate), 555 timer, a latching reply, a keypad and the normal assortment of LEDs, resistors, and capacitors to make a digital combination power lock. I elected to use SPST buttons vs the keypad as I already had enough and did not plan on making this experiment a permanent install.

Breadboarding this took some trial and error. I first tried to get it all on one breadboard as I was still messing around with experiment 18′s reaction timer on my quad breadboard. Things got really scrunched since I was using tactile buttons vs the keypad. 7 of the buttons serve the same function so I eliminated all but 1 and it still was a tight fit. After pulling things off an on several times to readjust for the lack of space the circuit worked but inconsistently. I traced the issue but could not find a way to fix it in the limited space, so I bid farewell to experiment 18 and moved this circuit to the larger board. Below is a picture of my layout.

The video walks through the operation of the circuit. Even after the move to the larger bread board I had some issues with the relay operating consistently. This was due it not getting enough power, my best guess was a less then fresh 9V battery was to blame.

Make Electronics Experiment 19 – Logic Gates

TheBFR — Tue, 02 Mar 2010 05:36:22 +0000

At the beginning of experiment 19 you setup the breadboard to have 5v DC by using a LM7805 voltage regulator, a .33uF cap, a 0.1uF cap and some jumper wires. The positive side of a 9V power source is connected to the Vin pin of the LM7805 and the negative side of the power source is connected to the ground pin. The ground pin (same pin as negative input) and Vout pin are then connected to he + & – rails of your breadboard. Ater making the connections and applying power I verified the voltage with a multimeter. This setup will be used quite a bit through the rest of the book. Platt explains that logic ICs such as the 74HC00 & 74HC08 have stricter requirements for input power then the 4026 CMOS chip used previously.

The rest of the circuit is pretty simple, containing 2 SPST buttons, 2 10k resistors, 1 1k resistor, a LED, jumper wire & a 74HC00 NAND gate for the first part and a 74HC08 AND gate for the second part. With the 74HC00 NAND chip the led is lit unless both buttons are pressed at the same time. With the 74HC08 the led only lights when both buttons are pressed. Platt does a fantastic job explaining NAND vs AND gates as well as the other styles of logic gates, OR, NOR, XOR, XNOR & NOT. This section is not lacking information and uses a lot of good figures to help solidify the difference between the gates. He also covers TTL vs CMOS, rules for connecting logic gates and gives a short quip on Bill Buzbee’s web server built out of 7400 series logic chips http://magic-1.org. So do yourself a favor and read the section before jumping to the next project.

I combined both parts of the experiment into one video. During the first part I incorrectly call the 7805 voltage regulator a 7508

Make Electronics Experiment 18 – Reaction Timer Part 3

TheBFR — Mon, 01 Mar 2010 04:24:20 +0000

The next evolution of experiment 18 is to change out button S3 that incremented the counter to a 555 timer (IC5) that will increment the counter for you. One less tired finger, one step closer to skynet…

The 555 timer is setup in astable mode by connecting pin 2 (trigger) to pin 6 (threshold). Also need are 2 resistors (1k & 2K2) and 2 capacitors (68uF & 0.1 uF). Button S1 will still pause the counter and button S2 still resets it. One thing I noticed is that sometimes when power is applied the counter is not starting at 0. I assume it is just leaving off where it last was, this is something I need to research further into.

Here is a video of the circuit with the 555 timer added

Next a second 555 timer is added (IC6). This time it is wired in bistable mode by applying constant negative voltage to pin 6 (threshold). This is done by connecting directly to ground & not using a capacitor like you would in monostable or astable mode. Two buttons are also connected to the 555 on to pin 2 (trigger) called S4 and pin 4 (reset) called S5. Platt gives a good explanation of how this creates a flip flop. These two button replace S1, so now a single press of S4 stops the counter and a pressing S5 restarts it. The output of the second 555 timer is connected to pin 2 of the 4026 (disable clock).

Here is a video of the circuit with the second 555 timer added

The last part of this experiment is to add a third 555 timer in monostable mode (IC7). This timer will act as a delay for starting the reaction timer. A button S4 is connected to pin 2 (trigger) of this timer and when pressed starts the delay. The length of the delay can be adjusted by changing the size of the capacitor (C5) that is connected to pin 6 (threshold). A led has also been added to let the user know when the counter starts. After pressing button S4 the user waits for the led to light then presses button S3 to stop the counter. S3 is connected to pin 2 of the second 555 that we added (IC6), when pressed the trigger (pin 2) goes low, sets the output (pin 3) to high, this stops the counter and also turns off the led. Lastly first 555 we added (IC5) that increments the counter needs some changes so the readout of the 7 segment leds are in microseconds. Per the book a 10k trimmer pot replaces resistor R8 that was connected between pins 7 & 8 on IC6. While calibrating the trimmer pot you replace the capacitor at C2 (pin 6 of IC5) with a 10 uF cap to slow the counter down. The objective is to get it to count in seconds, thus when C2 is changed back to 1 uF cap it will be in milliseconds. During the calibration the closest I could get was +/- 2 seconds, which then translated in to ~ 2 ms when the cap was changed back to 1 uF. The error gap was due to trimmer pot’s resistance making a large jump in the area close to where I needed to be. Maybe a different trimmer pot would have worked better but it was the only 10k one I had.

Here is the last video for this experiment

Overall this was a pretty educational project. There is a subsection in the chapter that talks about counters such as those used in clocks. While he mentions there are specialized chips to do this it would be interesting to figure out how to do it with normal counters. Figuring out how to make the second minute digit roll after 5, the first hour to go from 0 to 9 then to 0 to 2 before rolling back to 0 while incrementing the second hour digit between 0 & 1. I am beginning to learn that doing things like that is the best way to understand how more advanced chips work.

Make Electronics Experiment 18 – Reaction Timer Part 2

TheBFR — Sun, 28 Feb 2010 16:32:20 +0000

In next part part of experiment 18 we add 2 more 4026 counters to drive 2 more 7 segment leds (or the other 2 digits if you are using a single 3 digit unit). My leds read 90 deg off from the knightbright one when spanning the center of the breadboard (for better visual of this see video). After some trial and error with the layout I decided to put each of my leds with their respective 4026 on their own breadboard section. This layout allowed the leds to be read horizontally to each other vs stacked and also made for the best wiring layout. The 4026 chips were tied together by taking connecting pin 5 (carry output) of one chip to pin 1 (clock input) of the next. In this configuration when chip 1 (IC1) rolls from 9 back to 0 a pulse is sent out pin 5 to pin 1 on chip 2 (IC2) so that it increments it’s counter up one. The same thing happens when chip 2 rolls from 9 to 0, it sends a pulse out its pin 5 to pin 1 of chip 3 (IC3) causing chip 3 to increment its counter up one. Also added to the circuit were 2 more tactile buttons. The first was connected to the clock disable pin of IC1, which prevents the counter from incrementing while the button is held in it’s on position. The second button is connected to pin 15 (reset) of all 3 ICs. When pressed all 3 digits go back to 0.

Here is a video showing the operation of the circuit in this configuration.

Make Electronics Experiment 18 – Reaction Timer Part 1

TheBFR — Sun, 28 Feb 2010 04:43:38 +0000

The first part of experiment 18 is to test the function of your 7 segment led. Like I said in another post the 3 digit knightbright unit that I bought was common anode vs common cathode. The pin layout of my ca led is basically the same as what is shown in figure 4-33 on page 171 except that pins 3, 18, 19 and 26 are the common anodes. I placed the resistors at these pins and applied positive voltage, then with the negative lead tested each segment.

Before I continued I did a little investigating to see if I could use a common anode with the 4026 decade counter. I found some threads that showed how to do it but it seemed that another chip that I did not have would be required. Digging through my LED drawer I found two single digit units which both ended up being common cathode. I decided to use the one that came from Radio Shack since I could obtain two more locally (little did I know what an adventure hat would turn out to be).

The next part of the experiment just uses 1 of the 3 digits. I don’t have video of this part as I accidentally deleted it, but here is a picture of the end circuit.

The circuit consists of the 7 segment led, a 4026 CMOS chip, tactile button, a few capacitors and some jumper wire. This simple experiment is to show you the very basics of incrementing the digits on the led using the 4026. This is something I have to give Platt credit for. Breaking larger projects up in to smaller parts and then building it leads to less confusion and greater understanding of what the circuit is doing and how it is doing it.

7 segment led adventure

TheBFR — Sat, 20 Feb 2010 01:48:38 +0000

A few posts back I mentioned that I purchased the wrong 7 segment led for a project, common anode vs cathode. I decided that I would just pick a few up at Radio Shack vs ordering them to save on shipping. We have ~6-8 Shacks here in town and as luck would have it the only ones that had them were on the opposite side of town. I had time today to make the trip and wouldn’t you know mother nature decided to once again douse us with more snow. So I picked one that was the closest, wrangled up my son and made the 45 minute trip only to find they were out, my fault for not calling ahead. The guy was nice enough to check the other stores stock and found another that had more then I needed. So I headed that way, another 60 minute drive because of course it is in the opposite corner of town. Once I got there I had a hard time locating the store. The snow and peoples inability to drive in it did not help. I finally found the store thanks to google maps on my cell phone (yes I looked when parked) tucked away on a side street. They had what I needed and a few other items I did not but bought anyway. I made the return trip home through downtown in rush hour traffic, amidst a snow storm, 1h 15min. So that money I wanted to save on shipping got spent on gas and that wasting of 4 hours of my day. Oh well at least I have my parts and I got to spend time with my son.

Project V Video

TheBFR — Wed, 17 Feb 2010 00:01:50 +0000

I shot a 3 part video during the making of project V. The first covers initially setting up a simple circuit to light an array of 22 leds. The second part shows the pulsing circuit that I created using 2 555 ICs and the final part is the completion of the project.

Step away from the soldering iron

TheBFR — Tue, 16 Feb 2010 04:14:37 +0000

I told my wife that I had a dream last night about a circuit, one that I could not get to work. She laught and told me that I should take a night off from the electronics.

My mental anguish was due to the pre bed time discovery that a recently purchased 3 digit 7 segment LED display was common anode vs common cathode. It’s for a project in the Make: Electronics book and is to be used with a 4026 chip. So I am left to decide if I should just skip the project till I get another, just use a single digit 7segment common cathode and some leds or just order another one? I just ordered some stuff from mouser last week and padded it with a few extra things to make the shipping worth it so for now I will have make due.

So at least for tonight I am take a break… except for the fact I am reading up on AC power. We will see what I dream about tonight.

Project V & Blimpduino Update

TheBFR — Mon, 15 Feb 2010 05:10:09 +0000

So the blimpduino project is on hold for a bit. All I really need to do is fill the blimp with helium and connect the electronics to it. After pulling out the blimp this weekend and realizing how big it is, I decided I did not want to spend the $ to get it filled and then leave it laying around to slowly deflate. I would like to take it to work for a day once it is finished but want to wait till it warms up. By then it would need to be refilled, so for now test of the parts will have to patiently await their silver helium filled chariot.

I spent most of the week working on what I called project V, a Valentines present for my wife. I have been working with LEDs and the 555 chip, trying to make a pulsing matrix. After messing around with leds on a perf board I found that I could make a small heart out of 22 square 5mm leds. I used the projects from Make: Electronics and some others I found on Instructables as the basis for my circuit design.

Here is a snap shot of my initial cicuit mocked up on a breakbaord.

It is based off of Experiment 17 from Make: Electronics, replacing the speaker that was attached the the output pin of the second 555 IC with an array of 22 LEDs in a 3×6 + 2×4 configuration. While this circuit gave me my ~90% of desired results I decided to try and do that same with 1 less 555. After several days of trying different things, looking at posts and videos I was unable to find something that would work that way I needed it to. One circuit provided the desired effect… but not if I used all 22 LED’s. Any more then 12 and the pulsing became a solid on. I tried to find the reason, used my multimeter to find what was changing but in the end with my current skill level I was unable to overcome the hurdle and with Valentines just a few days away I decided to just go with a simple on off flashing circuit.I eneded up using amodified version of this circuit on Instructables. I just used 1 NPN and put my leds in a 2×11 array.

Friday night I started soldering the square leds onto a 276-149 perf board from radio shack. It quickly went down hill. The square leds I was hoping to use were hard to get straight and flat in a grouping. Reheating the perf board to adjust the leds was pulling up the solder pads from the board. Deciding that I needed to change my design I laid out a heart on another perf board with red 5mm dome leds I had just received from mouser. The new design had 18 leds, so I removed 4 leds from my breadboard proto circuit and made resistor adjustments as needed.

The dome leds went down much better, and by Saturday afternoon I had my heart soldered up with resistors.

The pictures show the front and the back of the led portion of the circuit. When connecting the leds in series of 2 (neg to pos) I tried to go above and below. The white wire was used for one pair that crossed others to prevent an accidental short. I then started in on recreating the circuit on 2nd perf board that would mount behind the leds.Here a few shots of the circuit.

I reused the original perf board from the square led debacle, which is why some of the solder pads appear to be missing. The circuit is pretty simple, and there was room at the bottom to mount a 9v battery. In hindsight I would have had the room to use the original dual 555 circuit so there may be some mods to the finial design in the future.

I put the 2 perf boards together with a set of stand offs and attached a 9v battery holder to the back with some hot glue… just in time to give it to my wife for Valentines day.

This was the first non kit, permanent project I have done. I have to say that even though there are a number of things I would like to do to improve it, I am still happy with the finished product.

Make: Electronics Experiment 17 tweaking

TheBFR — Thu, 11 Feb 2010 00:16:25 +0000

Experiment 17 is all about the 555 Timer IC, probably one of the most used IC’s. I gotta say after using the chip it is pretty easy to see why it is so popular.

You got to love a book that encourages experimentation and tweaking. Here is a video of experiment 17, mostly tweaking the finial project. It shows how changing/removing resistors and capacitors alters the sound and light pulses.