Category Archives: Electronics
Recently a friend gave me a broken Phillips AJ6111 radio. It was a neat little radio that you can mount under your kitchen cupboard. Only problem was that it didn’t work. I plugged it in, heard a click of a relay and the clock in front came on but none of the buttons seemed to do anything.
Now I’m no electronics expert but I do like to tinker. So I opened up the case and staying as far away from the 120V AC power supply as possible I started looking around. After poking around on the main board with my multimeter for a little bit it seemed like it wasn’t getting power.
So, I bit the bullet, unplugged the radio, discharged the capacitors on the power supply board and disconnected it.
I sat there and studied this thing for a while trying to figure out what it all did. I realized the AC mains came in and went to the smaller transformer first and a relay and then into some other circuit that probably only turned on the big transformer when the power button was hit. I’m sure people who know things about power supplies would immediately realize that this is a way to get standby power to power say the front clock while not turning on power to the whole thing. Regardless of getting a basic idea of what the circuit did what I noticed where two things.
First, there was a 1.6A 250V fuse that was blown, and second the two big capacitors on the board were bulging. Now I don’t have an EMR tester or anything like that but it was pretty clear these capacitors had gone kaput. So I ordered a new fuse and some 3300uF capacitors from Mouser. 5 minutes to install and now I’m the proud owner of a fully functional radio.
The point of posting this, is just to say hey, if you like electronics, you don’t need to be an expert or have a lot of fancy tools. Get in there and tinker!
Just a quick post about this awesome score I just made on Craigslist. I’ve been looking for a basic analog oscilloscope for a while. Everybody always seems to recommend the Tektronix 465. Go to eBay right now and you’ll see them selling from anywhere between $200 – $400 dollars. This seems ridiculous to me. Anyway I saw this on Craiglist the other day for $50 bucks and went straight out and picked it up.
This is a Tektronix 7633 modular oscilloscope. It came with a 7B53A Dual Time Base, a 7A18 75MHz Dual-Channel Amplifier and a 7A26 200 MHz Dual-Channel Amplifier. What all this means, is rather than just a basic two channel analog oscilloscope, I now have a fancy 4 channel scope with tons more functionality than a basic Tek 465. I’m still pouring over all the manuals but this thing has single shot triggers and does waveform storage of some sort and all sorts of stuff. Very fancy! New in the early 80s this baby cost anywhere from $5,000 – $10,000 dollars. Anyway, hopefully I’ll have more cool stuff to come using it.
So in the most recent edition of Circuit Cellar, one of the things in the “new things” column was a $150 dollar logic analyzer. Most logic analyzers are really expensive and since this one seemed affordable I decided to check it out. The Saleae website has better information that I could ever describe, but basically it was a USB, 8 Channel, 25Mhz logic analyzer with a really slick looking user interface. I decided I would order one and give it a try. I received mine within maybe 2-3 days so I was very happy about the fast shipping. I immediately set out to unpack the thing and connect it to something. The closest thing I had on hand was a toy Dora The Explorer phone. I quickly opened it up and hooked the analyzer up to the flash EEPROM chip in it.
Originally I tried using the logic analyzer on my Macbook using VMWare Fusion and although all the software installed fine, the USB didn’t play nice. I kept getting buffer overruns and errors about telling me that I needed to use lower sampling rate. I decided that the slowdown on the virtual machine and the VMWare USB probably was the cause so I decided to install the software on my main Windows XP machine. The software installed easily and the interface is dead simple to use. Even on my real Windows XP machine though I still get errors about needing to use a lower sampling rate. I got this even without anything else connected on USB and no other applications running. I was disappointed about this but I hope that future software updates will make this better.
Overall though I was extremely happy. I was able to capture the reading of data from the EEPROM when I hit the buttons on the phone. I can only assume that this EEPROM is where the voice data is stored. I’m not sure though if it just stores the customizable name voice data or also all voice data used. This toy uses a bunch of Winbond PowerSpeech chips and Winbond doesn’t make information easy to come buy. Very neat though. I was able to easily see the clocking in of the address and read out of the data.
I did manage to find a datasheet for the EEPROM so I knew the pins and then I wrote a python script to decode the logic analyzer data into a file for me. So now I can take a better look at what is stored in the EEPROM. I would imagine also now that knowing exactly how I should talk to this chip I could hook it up myself to a micro controller and read the complete contents from it. I can’t wait to use the logic analyzer for more things and I wouldn’t hesitate to recommend the Saleae Logic product to any other hobbyist on a budget.
I’ve also been looking into one of the VTech Apple toys. This toy also has buttons for each letter in the alphabet. The feel to the buttons on this toy is wonderful and I think rather than bend this I’d like to MIDIify it because it would make a rad drum controller. It wouldn’t be velocity sensative but still would be really neat.
This is a picture of the main board. What’s interesting about this is just like the vtech phonics pcb the main micro is on a separate board in the typical COB toy epoxy glob and then that breakout board just has a normal sort of DIP footprint soldered into the main board. I had not seen this before, but maybe since these are older toys this is what they used to do so they could re-use the same COB chip in multiple toys?
Here’s a shot of the main button board. I’m thinking I just need to throw an extra micro in the case and hook it up to the button board and then translate that to the MIDI messages. We’ll see how all of this goes.
One last quick thing. Anyone interested in awesome noise toys or just great kids toys should check out a recent post on GetLoFi. They tipped me off to Target selling $13 dollar touch sensitive toy guitars. I went out and bought one and it’s really amazing for only $13. I’m sure I could think of some great projects to do with it as well.
So, I’ve been working on a couple different toys lately. One of them is a VTech Phonics toys. It has all the letters of the alphabet on it and a couple different shape buttons. I started to take this apart and then didn’t have any pots or switches small enough to fit in the case. For now here’s a picture of the main PCB. If you follow the link I’ve annotated some of the pins on the Flickr page.
This was an awesome little weekend project. It consists of mainly a 556 IC which is really two timer chips stuck together. It pretty much creates square waves. there’s a volume knob on the side that doesn’t seem to be very volumy? Maybe because I stuck two speakers in the box making it 4 ohms instead of one 8 ohm speaker. The knobs on top are for frequency and time between the square wave samples. Fun little toy and a way to kill some time on a Sunday evening. I’ve got a really awsome V-Tech phonics toy from my daughters that I’m working on now too.
So at work yesterday we got a button. All it is, is a big purple Yahoo button that someone got for free. You press the button and it plays Yahooooo really loud. Pretty boring. I figured I would open it up and show people how to smash their fingers on the resistors to change the pitch.
So I unscrewed the thing and took a look. Pretty simple thing, of course the IC chip is a COB item underneath a blob of epoxy. This makes it really hard to figure out fun things. Someone then pointed out that there seemed to be a little 3 pin socket on the bottom of the thing. As I stared at the thing I saw that one of the pins was labeled Rec. Hmmm, I wondered if it would be possible to re-record the button to be even more obnoxious. I took a couple minutes and inspected the rest of the pins. I had two pins going to the switch to make the thing play. I had a Pl pin that if I jammed a wire between it and the positive power supply it would play. Alright Pl pin is a Play pin. It plays as long as you pull the pin high. There was the Rec pin, an IC pin a GND pin, two pins for the speaker and then a pin going to the resistor.
We sat for a while jamming wires on things and pressing our fingers on the resistor annoying everyone in the office. Then I finally tried connecting the Rec pin to the positive rail. Oops no more Yahooooo sound. I figured I blew something up. But wait I realized there was no more Yahoo but just a hissing. The I realized that the IC pin had a hidden letter and was really a Mic pin. Aha, I’m an idiot, so this turns out to be just a little 10 second recorder chip. All you need to do is pull the Rec pin high and input a mic or something else to the Mic pin and it will record.
We quickly cut up a mini jack cord, plugged it into my iPod and then touched the Rec pin to the power pin and it worked, kinda. It was way to quiet. I realized that I would need to bring the thing home and solder some proper wires to it in order to get good clear connections for recording. So I came home and started tweaking. First thing I did was reconnect the switch to the Play pin, this way when someone hit the button it would only play as long as the button was held down. Seemed like a good way to keep it less annoying if someone recorded something long. Second thing I did was to splice in a button between the Rec pin and the power supply. This way I didn’t have to hold some wire every time I wanted to record. Then I connected a mini jack connector to the Mic pin so it would be easier to record things. The final step was to take the Dremel and make some holes for the new input jack and button
It came out pretty good. The only problem was the button didn’t hot glue to the case very well. So I ended up just keeping it outside the case until I get something better to attach it. The only thing left that would be cool to do would be to get a decent variable resistor so you can mess with the pitch while holding the button. Over all, a fun little project for the night.
So I haven’t posted anything lately. And all in all I haven’t really finished any projects lately yet either. I haven’t made any headway on the frequency counter because I haven’t bought the parts I need. I did manage to snag some awesome old Atari joysticks at a church rummage sale. The plan is to convert them to wireless so they can control other things. Last week I attended TI Tech Days 2008. It was a good event. I didn’t pay anything because Digikey sent me a “don’t pay for this event” coupon in the email. They had some good talks on Zigbee and charging lithium ion batteries. I ordered up a neat like 40 dollar TI wireless dev kit that consists of a MSP430 chip and a CC2500 chip. I’m hoping that I can use those for the wireless Atari joy sticks. Also I’ve started building another robot.
My daughter has named him J-R. Couple things about him. His body is made of 1/16 inch aluminum, which sucks to cut and drill and bend when all you have is a hack saw, power drill and a counter edge. I went and picked up the aluminum pieces this weekend and since I’m sorta measurement retarded was surprised and how thick it was. Also there’s a couple parts made out of 1/4 inch aluminum bar and this time I was surprised at how small it was. I had to make the parts a couple times over because it was so tiny and the drill holes kept getting messed up. Overall he looks pretty good, not so straight, but straight enough. I have to get a Tamiya dual motor setup and a Sharp GP2D12 infrared sensor and then a bunch of various other components. I’m hoping I’ll be able to wire him up in the next month and then start programming.
Anyway, hopefully in the coming months I’ll get some more projects finished. So stay tuned
I started looking for a good radio frequency project. It just so happened that at the same time, everyone at work was interested in mini r/c helicopters and things like that. In my googling of everything r/c helicopter page ever, I came across a neat little r/c frequency checker for r/c airplanes. I also just happened to be reading some articles on superhet design. A r/c frequency checker seemed like a neat little project to try to do myself. So I set about starting to think about how I would build such a thing. The first thing that I figured I would need would be the LEDs. The r/c airplane spectrum starts at 72Mhz and each channel is 20Khz wide. All in all for airplanes there is a total of 50 channels so I would need 50 LED’s. I started to look around for a 10×5 LED matrix. My searches turned up nothing. Sure I could get a 8×8 LED Matrix and just not use the extra 14 leds but I didn’t think it would look as cool. So I set out to design my own. It seemed that If I designed mine so that it was just the LEDs and some pins on one board and all the control circuits on another board then I could re-use my LED matrix just like if I had bought one.
The way LED matrices work is all the anodes of a column are connected and all the cathodes of a row are connected. See the schematic below.
When you see the layout of the PCB you’ll see why I have the extra pins for the rows. Anyway when you want to display a certain set of LEDS you scan through each column enabling one column at a time and while each column is on you enable the correct rows corresponding to the LED you want on. If you cycle through all of the columns fast enough the eye thinks all the LEDs are really on at the same time.
I took this time to also teach myself EagleCAD since it’s free and there seem to be a lot of good tutorials on it. So I decided for the PCB that I would layout all the LEDS on one side and then put some breakway headers on the bottom side. This would then let me design a second board with female headers and all the LED controlling circuitry and RF circuitry on it.
I decided to keep all 10 pins for the rows even though I only have 5 rows just for stability when plugging into the second board. Overall I found EagleCAD easy to use. The schematic was really easy to draw up after getting the controls down. The PCB took a little more time but I think for my first attempt at a custom PCB it came out okay.
The real reason for this post is that I just got my custom PCBs in the mail and I wanted to share pictures.
I ordered 1 copy but ended up with 4 which was even better. The picture above is two of the PCBs one showing the front of the board and the other showing the back. Anyway check back for more posts as I assemble the LED matrix and the second board with all the controlling circuitry.
My daughter seems to be interested in robots so I set out to look for some sort of robot for her. Unfortunately there’s not a lot of stuff out there for a 3 year old. I figured that if nothing else I could build something and then let her play with it and tell her how it worked. I googled around for a bunch of stuff and eventually came across BEAM bots. They seemed nice and simple and interesting. I decided to order some solar panels from solarbotics and set out to build a trimet. I had just dismantled an old all in one radio, tape, cd player that was going in the garbage so I had managed to salvage a handful of motors from this. A trimet is real simple, you have a DC motor, you hook the solar panel up to some capacitors and then wire the capacitors to turn the motor on when they store up enough juice. It’s really a neat little thing. Here’s a picture of the guts of it all.
You can see the resistor, two transistors and the 1381 voltage detector underneath the solar panel. The body of the motor is used as ground for the circuit and then a paper clip ring is formed to be the postive rail. Then all the components hook up in the center and the solar panel on top. Here’s another shot of the trimet closed up.
The only thing I was really disappointed about was that there really hasn’t been a sunny enough day here to get the little thing going. It scoots around but not nearly as fast as if I just hooked up a straight 5v supply to it. I ordered up some extra solar panels so maybe I’ll make some other BEAM bots too.