Stuff going on

Well the Tropical Storm Erika has claimed down so now I can set my sights on some tinkering tomorrow.

For giggles I have been building a audible continuity tester to free up my single Multimeter.

The camcorder that I bought seems to be dead but I’m thinking to buy a power adapter for it to make sure. If it is dead I can reuse the power adapter for another project.

Tomorrow I’m going to start finishing the electronics portion of the CNC and make sure I don’t have to end up buying new stepper motors.

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Negative Voltage

I have seen quite a few questions on websites with people asking how to get a negative voltage to power opamps and such. Well I’m going to toss up a couple of ways on how to do this.

Batteries
Say you’re building a device that requires a LM741 opamp and want it battery powered. The LM741 needs a negative voltage on pin 4 of the IC. Now you need a minimum voltage for the circuit of say 3 volts or two AA batteries. In this case you would need four AA batteries to get a total of 6 volts. Now you wouldn’t be using the whole 6 volts but only 3 volts. The positive and negative for the positive rail would be two batteries and the negative would be the other two however the polarity would be reversed. This is a type of “Voltage Divider”.
batterydivider
The picture above are four AA batteries. The red lines represent the positive rails while the black and blue represent the ground/negative.

Power Supply – Wallwart type
Same issue but instead battery powered and want to use a wallwart style AC adapter. Lets say you need a total of 6 volts to power the circuit. You can use a 12 volt power supply and use a voltage divider circuit. Basically it consists of two resistors that form a virtual ground so the true ground turns into the negative rail.

Example

There are Voltage Divider calculators all over the net. Just google it and you will find them. Just enter the voltage and resistors and it will calculate the output voltages. You can even use this with batteries as well but you might get terrible battery life.

Dual bench power supply
Before you try this double check and make sure your power supply unit/s have “Floating Output”.
Floating Output is non-earth ground reference, meaning the DC ground does not share the AC ground.
To use this all you do is plug in one power supply into the other power supply. Not positive to positive and negative to negative but a single cable you plug into supply A negative and plug the other end into supply B positive.

Example

I hope this helps.

Really need a better power supply.

I bought a Sony HandyCam from a thrift store. It did not come with any cables let alone the charger, however it did have a battery. The battery cells are totally gone as well. Before sinking money into this camera and run into bad luck on finding out the camera is dead I want to power it up. I took apart the battery and removed the cells. Uses typical 3.7volt lithium cells. This makes the camera run at 7.2 volts. However there is a slight problem. The camera also needs a negative voltage. Sadly my power supply isn’t a variable power supply so I am stuck until I finish my new power supply.

Spent the day working on computers

Finished a project for a friend, built a PC from scrap parts. Typical AMD Phenom II with a HP motherboard, 4GB ram and with a Dell XPS 8300 case.
I also fixed up a HP XE793. Has a Celeron at 700MHz, 512MB ram, 160GB hard drive. While I was at it I yanked out the floppy and DVD drive. I then tossed in a Zip Drive, USB 2.0 card, 10/100 Ethernet and a 3com dial-up data/fax/voice modem that I plan to play around with. I’ll probably install Debian Linux on it or even dual boot a old version of Windows.

To put the cherry on the top I built a Faraday cage for my tinker PC’s SoundBlaster Live! card to block out EMF and AC bleeding for my oscilloscope. Works well and doesn’t pickup the AC current’s 50/60Hz.

Electronic part mods

Been tinkering away and got a nifty idea on a cheaper alternative to 10turn potentiometers. The small trim pots can be modified

You can easily turn these into their bigger brother trim pots. It’s the ability of a decent knob we’re after. You can carefully solder on a brass tube onto the little screw or use a cheap Alignment Tool that you can cut into the desired length and use some epoxy to secure it. To add a knob you just use a set-screw type but that can be very costly and will cost more then the trimmer. You could just use the Deremel on the shaft and grind down one side and use a cheap D-Shaft knob.

Another one is to extend a tactile switch. Use a long shaft switch with a wooden dowel rod cut to desired length and some heat shrink tubing to attach the two ends together. Sometimes you can’t have a switch on a front bezel unless you want a mess of wires. This comes in handy for kits that doesn’t come with a case as well.

I attempted to make a motorized potentiometer by using a PCB mount 10K ohm pot and a small shaker motor. The shaft of the pot is plastic so I was able to use some hot glue to fill the void of the shaft. I then drilled a small hole that was a little bigger then the shaft of the motor into the PCB portion of the pot. I put the pot back together then jammed the shaft of the motor into the hole that is parallel with the back of the pot’s shaft and then hot glued it all together. Everything works somewhat. The pot still functions but the motor isn’t powerful enough to turn the wiper of the pot. However the idea is solid and can be done with a stronger torque motor but it would work better with a stepper motor and a AVR to control it.

Ways to find free electronic parts

Best way to get Electronic parts is from old electronic devices that are ether broken or have no use. This little guide will list on what devices have what and so on.

Typical passive parts are plentiful in all electronics. Older devices are thru-hole and easy to salvage. I honestly avoid SMD/SMT parts. They’re a pain to remove let alone to solder begin with.

CRT TVs and Monitors are great for Power-Resistors, Voltage Regulators, huge Power-Transistors and sometimes Relays. Some people even reuse the flyback transformer for high voltage experiments. Take extreme caution, CRT TVs and Monitors are deadly if you go poking around inside if it hasn’t had time to discharge. I myself wait a day or two before hand and if I really need to get inside I will discharge the flyback primary to ground. Watch a couple of video on YouTube to see what I am talking about.

Flat screen TVs don’t really have anything to offer other then speakers and the power supply if it isn’t already dead.

Radios mostly have Crystals, BJT type Transistors, variable resistors and variable capacitors that are worth taking.

Power supplies at times have great stuff like the Transformer, Voltage Regulators, High-Voltage Capacitors and Diodes. Switching power supplies don’t offer much more other then Mosfets, negative Voltage Regulators, Fans and wiring. You can salvage typical stuff like resistors, caps and such but if you’re like me you’ll be up to your eyeballs in these parts by then.

Printers can have some great things. However I am not talking about that printer you bought right before Windows Vista came out and found out you can’t use it. I’m talking about fifth-teen years or older. You can get Motor controllers, stepper motors, brushless motors, belts and sometimes AVRs. A few times I found some GAL chips that come in handy for some old school 8-bit computing. Even Scanners of this vintage has the same stuff and if you are lucky a photocopier.

This maybe a sin to some people but old retro computers have a goldmine of 74 series and 4000 series logic for the taking. Also a good source for Tantalum capacitors, EPROMs and LEDs.

This may sound crazy but it is simply genius as well. Automotive junk yards are perfect for Wire, Relays, Solenoids, electric Pumps and Sensors. Most junkyards worry about the typical automotive parts like cylinder heads, seats alternators and such. If you walk up to the pay-booth with a box of wire, sensors and relays they will most likely pull a number out of their butt and typically a low price deal of $20.00. However fuel pumps and solenoids might matter and they might have a higher pricing point. You never know and most junkyards will have pricing sheets to give you a idea.

Most modern electronics are not worth messing with for salvaging parts due to being SMD type and sometimes you will run into parts that the datasheet is only in Chinese or never find any info at all. A lot of older electronics also don’t use jellybean parts like 2n3904 transistors and use some off the wall cheaper version that is some what compatible. This is why the internet is great for looking up stuff and if you get stuck a transistor tester from eBay can tell you.

Spindle control sadness

Wanted a PWM spindle control but the motor I have chosen sucks too many amps so I am stuck using a TIP122 transistor to act as a switch with the arduino. Works like a charm and the transistor only gets warm to the touch with a small heatsink. I guess it will work for now.

Tool Tuesday 8/18/2015

Kinda late on this week’s entry but life goes on.

Lets talk about Logic Probes and Pulse Probes.
This handy dandy devices are a bit old school but still come in handy if you don’t have a logic analyzer or oscilloscope. They are used for probing digital circuits for the boolean 0 – 1 or “high and low” states of a digital chip. Since everyone is on the AVR route of things this devices come in handy for quick troubleshooting before resorting to looking at code to see if you missed something. Most Logic probes can be set for TTL (transistor-transistor logic) or CMOS (complementary metal-oxide semiconductor) states. The probe has three LEDs. One for High status, one for low status and one for a NOID like light for pulse. A pulse probe is pretty much a logic probe but you can send out a pulse and have a logic probe pick it up to test a chip or even a transistor to make sure it still works. Some higher end probes have piezo buzzer that will give off different tones for high and low pluses. The Pulse Probe or Pulser for short is capable of clocking digital circuits – the signals are at LOGIC LEVEL.. The Pulser can also be called a SIGNAL INJECTOR however the term Signal Injector normally refers to an audio or RF signal injector and these have a low output (amplitude) and the waveform will not (may not) clock a digital circuit.

You can even build a simple logic probe with some resistors and LEDs. However that is more of a test NOID light and doesn’t work as well. If you really want to build a decent one try this schematic.

I built one a while back and used a 2n2222 instead of a 2m2219a transistor.

Bench supply

Found a nifty Arduino controller for a power supply. The person that created it also has included some PC controlled software for it as well. Instead of using ATX power supplies I’ll just use off the shelf laptop based chargers to minimize the overall size. Toss on a LM317 or LM338, a 10 turn pot and the Arduino. Also instead of having it in one single unit I’ll fabricate a stackable cases.

New bench power supply

I am in need of a dual bench power supply with floating outputs. So since I have a few computer ATX power supplies laying around I can modify them and use them.

Typical ATX power supplies out of the box are not really floating/isolated. The DC ground is shared with the Earth ground. The Earth ground comes from the mains input and connects to the casing while the power supply’s PCB is then mounted to the metal casing expect one or two screw portions have electrical pads that run to DC ground. All that is needed is to use a multimeter to find these points then insulate the pads. Well for my project I plan to use a custom case to house both supplies. I might also have a banana plug for Earth ground to be isolated or not. The supplies will not be in series or parallel. I also plan to only use the 12volt and ground rails with a LM317 regulator with some 10turn pots, maybe some rotary encoders and LCDs to display Voltage Current. Might give me a reason to buy a Arduino Nano.