Shawnville » Electronics

Droid X

Shawn — Mon, 20 Sep 2010 00:47:36 +0000

Here is another test post from my Droid X.

Android

Shawn — Mon, 20 Sep 2010 00:34:41 +0000

Posting this from my new Droid X. Using the wordpress app.

Dome Light Dimmer

Shawn — Sun, 03 Jan 2010 05:45:46 +0000

I have been trying to replicate the interior light functions of some of the newer cars for some time now. I like how they stay on after the door is closed and then fade away. This is also called theater lighting.

This circuit is based around the ever usefull 555 timer, and an N channel MOSFET.

I am building this for my 1969 Chevelle. Dakota Digital has something similar, but I didn’t want to spend $200 on it. I am working on replicating the retained accessory power too.

Here is the circuit on a prototyping breadboard.

The capacitor (C2) & resistor (R4) connected to pins 6 & 7 on the 555 timer controls how long the output on pin 3 is high. A larger capacitor or more resistance will give you more time.

The fade effect comes from capacitor (C1) and resistor (R1), which pulls the voltage down slowly.

Dome Light Delay / Dimmer v3 Schematic

K1: Switches on the doors connecting the trigger to ground.
K2: Ignition switch to cancel the circuit — turn lights off immediately, unless doors are open.

Q1: 2N7000 MOSFET
Q2: NPN 2222 Transistor
U1: 555 Timer
C1: 22uF Capacitor
C2: 100uF Capacitor
C3: .02uF Ceramic Disc Capacitor
R1: 447K Ohm 1/4 Watt Resistor
R2: 1K Ohm 1/4 Watt Resistor
R3: 1K Ohm 1/4 Watt Resistor
R4: 10K Ohm 1/4 Watt Resistor
R5: 1M Ohm 1/4 Watt Resistor
R6: 1K Ohm 1/4 Watt Resistor
D1: 1N914 Diode
D2: 1N914 Diode

RCA HD52W58 TV

Shawn — Thu, 22 Oct 2009 01:13:29 +0000

Today I fixed my Parents’ RCA TV. It has a problem that a lot of RCA TVs have in this model line. The Horizontal Output Transistor goes out and the TV will not power on. Instead it just makes a high pitched sound and clicks (that is the flyback trying to start).

Here is the Horizontal Output Transistor. If it is bad, it will check shorted between all three pins (that’s 0 Ohms resistance). I got this part from a local parts supplier for around $9.

This is the high voltage board from the TV. Notice I said “HIGH VOLTAGE”, be very careful playing with this board, especially the capacitors (left in the picture) and the flyback (right in the picture). And of course you never want to work on the TV while plugged up to power.

The part we are after is attached to the big heat sink (the one at the bottom of the picture). It is easier to remove the solder from the three pins while the transistor is still attached to the heat sink. I use solder wick, but you could use a De-soldering pump. Wick is easier for me.

Here I have highlighted the three pins of the transistor that have to be de-soldered. You can also check the transistor here. If all three pins are not shorted to each other, your problem may be somewhere else.

Here is the disclaimer: this seems to be a temporarily permanent fix. I have replaced this transistor 3 times now, about once a year, so there is still something in there that is not playing nice with the Horizontal Output Transistor. But, $9 a year is still better than $1000 for a new TV, especially since this TV still has a very good picture.