Here are some equations for current sense resistor:

$$R_{sense}=\frac{1}{I_{trip}}$$

$$P_{sense}=I_{trip}^2R_{sense}$$

$$V_{max}=\sqrt{R_{sense}P_{sense}}$$

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What you need

• A soldering iron
• 2.2k resistor(Optional power led resistor)
• a LED or more(if you want lighted Cigrette lighted sockets)
• A Resistor that is $$\frac{12_{V}-(n*V_{F})}{I_{F}}$$ Where Vf is the LED Voltage Drop, n is the number of LEDs and If is current usually 20mA
• DC-DC boost converter that outputs the same voltage as your charger but runs on 12vdc
• A spear ac adapter to salvage the connector that fits the computer(I used one from a old motorola cellphone charger adaptor that I got from a hamfest)
• Cigrette ligher cable. Got that from the hamfest as well!
• Female Cigrette lighter connector I got two of them with 3 connectors each for free.
• Heatshrink tubes(Prevents short circuits)

My chromebook uses 19VDC @ 2.31A so I looked at eBay for a boost converter, this is because car voltage is only 12VDC it needs to be stepped up. The chromebook may run from 12VDC directly it probably won’t charge. I got a 3 female Cigarette lighter socket from a hamfest and add 3-green LED in series with a 240-ohm resistors and put them close to the hole in the middle of socket, making the sockets lighted.

Steps

1. Cut the cord with the end that fits the computer. DO NOT CUT IT TOO SHORT BECAUSE WE WILL USE THAT PIECE TO ATTACH THE BOOST CONVERTER TO THE COMPUTER.
2. Use your multimeter to find the wire that goes to the tip(Center usually +) and the sleeve(Usually ground). Solder them to the output of boost converter. You may want to attach it to a insulator on copper tape if your going to add a LED.
3. Connect the LED with the anode(before the arrow on the LED symbol) to resistor and +Vout and cathode(the line, after the arrow symbol) to ground This LED lets you know if its on, wired correctly and has enough juice to power the computer(it will flicker/blink if the computer overloads the boost converter
4. If you want to light up the cigarette lighter female plug just put them close to hole where the center +12v is. You can wire them in series for multiple jacks, like in the circuit below. The formula for the resistor is $$R_{1}=\frac{12-(V_{F}*n)}{I_{F}}$$ where Vf is the forward voltage drop n is the number of LEDs and If is forward current.

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Addition

Addition is very simple! To do it just connect some pots in series. With series resistors their resistance adds up.

Subtraction

NOTE: If there are 3 or more pots in series, just set them all the way down to 0 ohms.

Multiply

Again if there are any unused pots set them to 0

Divide

In this animated circuit shows you how the resistors divide the voltage. The resistance isn’t important. You probably want nothing lower than 2.2k(for 32.5v, which is probably the max my adjustable voltage source will give you.) To figure out the current rating use this equation $$I_{max}=\frac{V_{in}}{R}$$ To use that circuit first measure the voltage source output(The numerator of the fraction). Then tap into the resistor chain(the denominator of the fraction). The voltage output from the resistor chain will be the Quotient. You can use any number of fixed resistors and any reasonable value as long is impedance doesn’t go too high where the current is too weak for your meter to pickup. You also don’t want to go too low where your batteries leak or explode or even the resistors could catch on fire if the wattage goes over the rated resistor wattage.

The adjustable voltage source

Here it is. This will give the numerator any number between 1.25 to 32.5. I plan on powering it from 4x 9v batteries. This will provide 36vdc of power. You can use anything from 40v or less. If anything higher is needed you can build a rectifier diode chain, I’m not sure if it’s accuracy is any good. Any adjustable linear voltage regulator is good for this purpose To change the voltage range on the LM317 click here.

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System Requirements

Windows 2000 or higher (32-bit Windows recommended)

A parallel port that supports the registers (most USB adaptors do not support it, they only support printers)

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The post Resistor RJ45 Tester first appeared on Delphijustin industries.

• 1x dc blocking capacitor(10nF to 10uF) C3(2.2uF Axiel Film Capacitor)
• 2x 100nF Capacitors C1 and C2
• 2x 1k ohm resistors R1 and R2
• 2x 4.7k ohm resistors R3 and R4
• 2x General Purpose NPN low power transistors Q1 and Q2(I used PN2222A)
• A 1.2 to 14v dc power source
• A alligator ground clip

This signal injector can come in handy for repairing radios, amplifers and old TVs and also square wave generator in a probe. Later on I will make a version that uses C1 and C2 as 470nF and R3 and R4 as 1 Megaohm and C3 as 47uF(Since the frequency is ultralow).

The specs

Where R=R2 or R3, C=C1 or C2 and \(C_{3}\)=C3

Frequency: \(f=\frac{1}{1.38RC}=1.5kHz\)

Output AC Resistance: \(X_{C3}=\frac{1}{2\pi*fC_{3}}\)

PCB Files

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This is a simple wire tester all you need is a 12-1000vac non-contact voltage detector. The ideal is to connect AC live wire to the red circle is. You do not use ground or neutral wires, these wires should be cut off. If the cord is shielded(coax) the detector doesn’t. Even though there’s only one wire used you should not touch the wire. The 5v is actually the ac mains voltage. The three switches choose 1 out of 8 outputs to connect the ac live wire to.

Whats needed

• 1x spdt switch
• 1x dpdt switch
• 1x 4pdt switch
• 1x RJ45 Jack
• 1x Polarized ac power cord
• a project box that is big enough to fit everything
• MultiMeter
• screwdriver
• drill

1. drill holes in the box for wires and switches
2. connect all switches as shown in the picture at the top. NOTE THAT THE LAST SWITCH OUTPUTS GO TO THE RJ45 JACK
3. Next set your multimeter to lowest resistance range and check for continuity between live wire pin and rj45 connector. this will help find the correct pinout on the switches

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Parts list

1x USB Extension Cord

cheap heatshrink assortment

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It uses a switching transistor to turn the buzzer on and off. It’s best to use a transistor since it can take very little current to turn on. It needs a SPDT magnet alarm switch since it has to switch the capacitor between +v and transistor base resistor. You cannot use a SPST switch. I didn’t need a transistor for the buzzer since it didn’t need alot of current.

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It hooks up to the tv and allows you to play 5 different types of video poker games. The game is in black and white and some of the suits look funny. The pinouts can be found in README.MD file.

Youtube videos

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