Exploding servos

Jun 172012
 

Last night I started working on a servo tester using the 555 timer. As I am doing more with servos as of late I felt a stand alone servo tester would serve me well in the future. Schematics and board art will be uploaded later in the week when I can finish it and tweak a few things. Today after work I decided I should add a transistor to the schematic for larger servos and loads. It worked. A bit too well in fact. You can see the damage in the pictures below

As you can see the transistor worked. A bit too well. I can only guess at the voltages but it was a bit intense. Loud pops, lots of smoke and bubbled plastic. Its ok I suppose. That servo was starting to annoy me.

Cheap-O power supply

Jun 062012
 

You see them all the time from fresh faced EE students looking to power their new arduinos and LED’s. The simple computer power supply hacked and forged into a fixed output power supply for a range of very common voltages. Which is exactly why I did the same thing. I like my design, rather than trying to cram it all into the PSU case I attached a piece of bent Lexan to the underside of the case and brought all the wires out. I’ve got all the common voltages, and this supply has two different 12v outputs. Later on I may open it back up and throw an LM317 on that second rail for a variable voltage.

I didn’t take any pictures of the bending process but its stupidly simple. Find where you want the bend and add about 1/4 inch (6.4 mm for my metric friends). Then place the sheet in a vice and use a heat gun to heat the joint up. Keep the heat even or the plastic will bubble and ruin. Eventually the weight of the Lexan will cause it to bend at the vice. Just hold it in place for a minute until it cools.

Z80 computer – The Start

Mar 102012
 

Yesterday I went to my local Hamfest and picked up a few Z80 Processors and other goodies. While reading the datasheet I noticed something. If the data lines for the z80 are held in an active low state I will send the CPU a series of NOP (No-Operation) commands. A quick glance on the internet confirmed this and I quickly breadboarded a prototype. I used a manual pulsar as the clock source, tied data lines down and sent the four least significant bits of the address lines out to some LED’s.

 

When the CPU came up I was able to pulse and the CPU went through the reset cycle. This is great, I know the z80 works and I’m taking my first steps toward building a computer.

I’ll build a dedicated clock and RTC next.

Fail better

Feb 202012
 

“Ever tried. Ever failed. No matter. Try again. Fail again. Fail better.” – Samuel Beckett (Westward Ho)

 

I’ve spent a long time trying to etch my own boards only to end up with a pile of mush on my copper clad. My main issue is getting the board hot enough to melt the resist off the transfer paper and onto the copper. Recently I’ve tried it all paper, photo paper, magazine paper, and the list goes on. I’ve tried preheating my board, using the iron for a longer period of time (Which just happened to transfer the ink onto the copper but melted it too much and ended up with an usable trace).

I wanted something simple and easy to try so a few weeks back I saw a hackaday post about LiPo battery chargers that plugged into the USB port. In the comments I found this version which I liked because it had the USb port built in. So I set to work. I tried preheating again with my hot air gun and got the board scorching hot. Laid my piece of transparency down and started ironing. A few minutes of that and I blasted it again with the heat gun until the plastic peeled away and left the ink on the board. FINALLY! After so long I did it. The actual etching its self was trivial, and I got my first real attempt at soldering SMD parts. However until the resistors (That I’ve been waiting on for two months) get here I can’t do much more with this board.

SN754410 motor controller

Nov 012011
 

An H-bridge is a circuit designed to reverse the polarity on a load, usually a motor. With the spectacular failure of my PCB etching and time until the robot competition growing shorter I’ve decided to build it on a piece of perf board. My skills in this area are pretty bad.  I used a Sn754410 IC, a common IC for the job. I’ve also added diodes to prevent fly back. But I may end up replacing the diode I’ve selected, I think they may be a bit over kill and the voltage drop on them is larger than I would like.

I’ve uploaded my simple schematic here feel free to use it.

 


BEHOLD! A new PCB is born

Oct 292011
 

Or not. I’ve spent the last three days trying, very unsuccessfully to transfer my design for a sumo bot onto a piece of copper clad. The result of this time? The image on the left. A cup coaster I’ve spent the last 2 hours laboring over trying to etch. Maybe it was the lower quality paper I used to transfer. I’ve tried everything from photo glossy to a comic book I had. Various printer settings and various board treatments. I believe heating the board and then pre etching it with Ferric Chloride (or etchent of choice) actually helped quite a bit. I actually got the design to stick this time. My alignment isn’t so bad. Nothing should short with the etches on the other side but it’s still pretty horrible. I’ve got two more weeks to build this. Although this was a failure. I did learn a few things. With my next attempt it will work. This may be a failure, but it was one I could learn from