More part salvage

Had a little 13inch color TV that was from 1984 and stripped it down. Got all kinds of transistors, power resistors, caps and pots. Also a couple of logic gates that were a bit too easy to take off. You can get all kinds of parts from old CRT TVs.

Advertisements

Tool Tusday 7/28/15

DIY LCR Transistor kit.

I bought one of these kits. I must say it is easy to build and a novice can tackle it easily. Just keep the multimeter on hand because some of these resistors are hard to identify. The kit is based off of a ATMega328p Micro and a bunch of 1% resistors. The LCD is nice, has a bright blue background and white text so it is easy on the eyes.

LCR1  LCR2LCR3

On my build I left out the 9v battery connection and used a 9v wall-wart instead. Calibration was a bit daunting but I finally got it to calibrate. The down side is it uses a screw terminal to plug in the device on test. I’m thinking to build a case and use alligator clips as the test leads. In all I think everyone should have one of these, should be as important as a multimeter.

Not a good day

Every PWM 555 timer circuit I have tried does not work. It only varies about a volt difference. So after wasting a day on this I’m just going to use a fixed speed system. Just use a rotary switch to switch between voltages for the motor. I think I’ll have a four voltage selection of 5,8,10,12.

More CNC spindle + new toy

The schematic I posted for the spindle doesn’t work well. Only puts a duty cycle of 75% to 95%. So I am still searching on one that will work from 0 or 10% to 95%.

Last night I tried to order one of those Arduino DIY LCR/transistor testers and had issues with my bank for the order. So after fighting the bank and them flat out telling me I can’t do international transactions (Never use a bank that is only located in one state) I found a loophole. Wired money from the account to my paypal and bought it that way. Should be here in a week and when it gets here I’ll do a step by step build with pictures since there is a lack of pictures / tutorials on my blog.

More CNC 7/21/15

This Friday I will be prototyping the spindle control. It will be a PWM configuration using a 555 Timer and IRF510 Mosfet. The schematic I found uses a diode to protect the circuit from the motor but it doesn’t say what kind of diode. It lists a 1n4148 diodes for other parts of the schematic but I doubt it will work well for this so I might use a 1n4001.
Diagram

I rather control the spindle speed by hand then having the main controller doing it. I plan to use 5volts to power the PWM circuit and 12volts to power the spindle itself.

Tool Tuesday 7/21/15

Lets talk Drills.

Lets start with pros and cons of Cordless drills. You can go buy a cheap drill and ten years from now still get a replacement battery for it. You can buy a high end Makita drill or even a middle grade Craftsmen brand and be lucky to get replacement batteries for three to four years before they redesign it and you’re stuck buying a new drill or you can reverse engineer a battery.

Cheap drills can only do so much before you end up getting upset with your self and have that moment “I should of spent that extra thirty dollars!”. They use a lower voltage, amp and current. The torque is about the same as a baby’s grip. Most of all cheap ones from say Harbor Freight will blow up during use.

Regardless you be happier with a mid grade or high end drill.

Everyone has their own preference on cordless drills. I myself have a Craftsmen drill that was left to me by my late father. The drill had two battery units and one lasted ten years and the other lasted thirteen years. The only thing I didn’t like about it is when I needed it the battery would be dead because it used old school NICD cells. So if I wanted to use the cordless I had to plan ahead three hours. However I have a Skil 6340 3.5amp 0-1300 RPM corded style drill with a 3/8 key-less chuck. Had it for twenty years or so.
Skil Drill

Only issue I have with a corded drill is the power cable is only three feet long so if I need to use it I have to lug around a extension cable.

Now if you’re in the market for a drill I would suggest to get a cordless that uses Lithium cells. So if you are like me you can charge it and when needed it will still have juice in the battery up to I think three months. It’s up to you on the bells and whistles let alone the brand of drill you are looking for. I myself tried Ryobi, DeWalt, Makita, Craftsmen, Black & Decker and out of all of those I prefer the Makita. Some drills have a bubble level on the end so you can make sure you’re level. Some have smaller sized chucks and others can hold monster sized bits. Today’s drills have Micro controllers that stop the user from abusing the drill that help prolong the life of the drill and to help the company that made the thing drop down in replacements/refunds. Makes it a love/hate relation ship because sometimes you need to drill something that will take a lot out of a drill.

It doesn’t hurt to have a corded drill. They come in handy and work great for mundane things. There is a guy on YouTube that builds projects that involves a drill to work as a lathe or even a jig saw.

Here are some tips for drills.
Keep the drill bits well oiled. Buy a quick changer bit so you can switch out bits on the fly. Mount a small block of wood to the top to always make perfect straight holes or build a jig if you don’t want to hurt the drill’s casing. Never leave a battery in the charger longer then the recommended charge time. So don’t think “hey, I’ll leave it in the charger when not in use”. Smart chargers will drain the battery and recharge or stop charging, let the battery discharge then charge again. This will degrade the battery real quick. Store the drill in a dry place, do not store it in a shed or garage.

Recycling Electronics

To save some cash on hobby electronics I attend to salvage parts from broken or unwanted PCBs. Some parts only save you a few cents but at times it can save you a couple of dollars. When you run across parts yo wouldn’t want such as transformers, coils and even wire you can recycle them. The catch is it much be copper. I started to do this recently when I took apart a old CRT. Just unwrap the copper windings from a transformer and there you have it.

When salvaging parts be ready to google datasheets for ICs and power transistors/mosfets. Sometimes they’re worth keeping and other times if you can only find datasheets in Chinese or no info on the item you can just skip them.

Here is a short list of parts I keep. 99% of the stuff I salvage is thru-hole, no SMD crap.

Coils / Inductors (at times they cost a nice chunk since it is copper magnet wire.)
Capacitors
1Watt or higher resistors
Diodes of all shapes and sizes
Big power transistors and fets
Crystals
Audio jacks
Variable resistors and capacitors
Voltage regulators
Ribbon cable
Jumpers
ICs such as PWM controllers and so forth
Motors
Heat-sinks
Screws and nuts
Ferrites
LEDs
Switches
Piezo buzzers/discs
Power cables
Relays

The easiest way I have found to strip boards is to use a cheap soldering iron, surgical claps and solder to remove ICs. Sometimes a small jewelers screw driver comes in handy to lift IC chips. When in a pinch I’ll use a small pair of needle nose pliers to get a better grip on a part. Just make sure you don’t squeeze too much on the handle. If you have a rubber band handy you can use it on the handle to use it like vice grips.

Parts I skip when salvaging.

Small transistors
1/2 watt and smaller resistors
Ferrite jumper beads
cable connector headers (They always melt or deform)
jumper wire
Parts that have no description

8inch B&W TV modding

Bought a 8inch B&W TV/Radio for a project a while back. I decided to add component video to it. The TV uses the typical KA2915 all-in-one IC. When researching this I came across a video where some kid did this to a TV but when I tried it didn’t work. I was about to give up when a alligator clip tapped the trace I cut off and presto I had video. Now to cram it back into it’s case and store it for when it is time to build my retro computer.

Switch-mode power supplies

I have been thinking on a power supply for the CNC. I was going to tackle a Linear power supply but that’s too much work and by time I’m finished it would be too big and heavy from a beefy transformer. So comes to mine a switch-mode power supply. If you didn’t know computers use switching power supplies. Starts out kinda Linear like but in a nut shell uses a form of PWM (Pulse Width Modulation). Lets you have more power in a smaller package and has more bells and whistles such as over current protection and so forth.

Lets have a quick rundown on a typical PC ATX switch-mode power supply. I’m not talking about a Cosair 1000watt dual 12volt rail, just a typical one you would replace when upgrading a PC.

They’re typically dual channel/rail. One rail for 12v and one for 5v. This was the standard for the much older AT style and for ATX they tossed in a 3.3v but it is tapped into the 5v rail with ether a linear voltage regulator or some sort of rectification. Over time other stuff was added such as the +5VSB (5 Volt Standby) that even when the system is completely off 5v is still surging around the power supply to ether keep CMOS in check, Wake on Lan running or for today powering USB devices such as keyboards. There is much changed in ATX 1.0 and ATX 2.0 specs other then four extra pins were added from 20pin to 24pin. If you want to know more history on it check out Wikipedia.

So if you want to convert a switch-mode power supply for a project here are some key items to look for. Even if it is a cheap power supply and doesn’t have them all isn’t lost and you might be able to add them.

MOV (Metal Oxide Varistor)
This little blue like disk suppresses voltage spikes. Pretty much the same thing used in power surge protectors. There are two of them connected to each Live and Neutral lines to Earth ground. I typically keep old ones from stuff I tear down. Sometimes a supply will have a ton of them. Before rectification and after. Sometimes for each rail/channel. You can get away from using a surge protector but I wouldn’t recommend it since they don’t handle brownouts, over current from a short circuit.

Transient Filter
It’s a filter to suppress noise from the switching transistors and noise in the mains AC line. I’ve came across a couple of PSUs where this filter was not available and did mess with other equipment such as a TV and made the video a tad snow like and added a audible tone from the speaker.

the problem with PSUs is that their switching transistors produce EMI/RFI that could seriously affect other electronic devices in the house. Also we must protect the PSU from incoming noise and voltage spikes coming out of the power grid, so the role of this stage is twofold and serves as protection in both directions.
Noise can be classified into two types, according to the conduction mode: Common Mode Noise (CMN) and Differential Mode Noise (DMN).

  1. CMN is electrical interference with reference to the ground or common wire. It consists of high frequency spikes and comes from faulty wires or from EMI/RFI of nearby devices. Common mode choke coils along with Y capacitors are used to suppress CMN.
  2. DMN represents the noise that is measured between two lines with respect to a common reference point, excluding common-mode noise. To suppress DMN, X capacitors are placed across the lines.

The EMI/Transient filter in PSUs is always placed before the bridge rectifier, because in this position it also suppresses the noise coming from the bridge’s diodes (yes, even those produce noise, especially at the moment they are turning off). The necessary parts for a proper EMI/Transient filter are two Y and two X capacitors, two coils, an MOV (Metal Oxide Varistor) and a fuse. Very briefly an MOV is a voltage-dependent resistor that protects the PSU/system from voltage spikes coming from the power grid. However, especially in low-end PSUs, manufacturers omit some components in order to save money. Usually the first to be left out is the MOV. If your PSU does not have an MOV in the EMI/Transient filter then you should always operate it along with a surge protector or a UPS, otherwise a spike could damage permanently not only the PSU but your project too. There is typically a Thermistor in the mix as well. After the EMI/Transient filter an NTC (Negative Temperature Coefficient) thermistor is usually used to protect the other components from large inrush currents. A thermistor is simply a resistor that adjusts its resistance according to its operating temperature. The resistance of a “cold” thermistor is usually 6-12 Ohms and after the start up of the PSU the thermistor heats up and lowers its resistance to approximately 0.5 to 1 Ohm.
High efficiency power supplies use a relay that bypasses the thermistor after the PSU starts up, in order for the thermistor to cool down and operate normally in a hot switch restart (off/on) of the PSU. Also by bypassing the thermistor efficiency is improved a little bit since no energy is wasted by heating the resistor.

Fuse
Most decent PSUs have a fuse. However cheap ones from China like to skip this and you can’t really add a fuse to the PCB of the supply but you can add one to the Live lead or a fuse to the device you want to power. If you came across a PSU with a blown fuse I wouldn’t recommend on using it because there is a chance it will blow again when replaced since chances are there is something else dead or dieing in the PSU.

Capacitors
These PSUs use a ton of electrolytic capacitors. If it is a older unit check them out visually to see if they have burst. If the top of a electrolytic cap isn’t flat then it needs replacing. I prefer to use Rubycon brand caps. When re-capping make sure to use the rated size. You can go higher on the voltage but don’t go under. So if you needed to replace a 1uF cap rated at 25v you can use a 1uF cap rated at 50v. However these can be a little fussy so try your best to stay within the voltage rating.

That is what I look for when choosing a PSU for projects. If they do not meet my preferences I’ll see if I can make the changes and if not I’ll just strip them down and use the parts for other projects. Sometimes you can get some nice mosfets and voltage regulators from these, not to mention resistors, diodes and caps.

To make things clear you can’t really do much with switch-mode power supplies parts such as the transformers and a few coils because unlike a typical transformer they use different signals on the output.

Wish there was a way to identify a transformer

Took a old radio that didn’t work apart a while back and came across a part of the power supply today that was stored in a box. My guess by looking at the transformer it steps down 120v to 12v – 24v. The problem I am facing to is to identify on how many watts and what not it supports. I’ve googled everything from the transformer and PCB that is mounted to it with no luck. I’ve contacted RCA and gave them the info of the radio I pulled it from and I get the ye olde “We’re sorry but that product has been discontinued. Please look at our new products, here is a list of retailers”.