Simplest Intercom

Using old phones

Using your old phones, you could create personal "micro" telephone exchange as simple as above circuit.
I manage to solder the test circuit less than a minute. Than connect the phone and test it.
It works. So why 39 ohm?
From
Epanorama Dot Net,
the correct value of the resistor should be a resistor that can limit the circuit current around 30mA total loop.
The method is by replacing the resistor in the circuit with a variable resistor, plug in the phones, apply power and tune the current
with the variable resistor so the current flow is 30mA.
After that take out the variable resistor and measure the resistance/ohm across it.
Find the fixed resistor with the nearest ohm reading to it and replace it to the circuit.

Simplest Circuit

Testing In Progress

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Simple Cable Tester

Simple DIY Cable Continuity Tester

How to use

This simple cable tester can be used to check 2 wire cable such as coax cable, telephone cable, audio cable and etc.
Power the circuit using 9V battery.
Plug in the cable and push "TEST" button.
The dummy resistor is connected to the end of the cable which has 75ohm resistor inside.
The tester will show only 3 conditions, "SHORT", "OPEN" and "GOOD".

How it works

The method is to check resistance of the dummy resistor at the "Terminator".
The idea is simple.
Imagine there is a short circuit cable under testing.
The wire will act as nearly zero ohm resistor thus making the voltage divider near the dummy resistor to divide the 9V into 4.5V.
Calculate it your self [ ( 1k / ( 1k + 1k ) ) * 9V = 4.5V ].
4.5V is below than the lower "Comparator" limit (Vref 4.57V).
It will trigger the lower "Comparator" and make "Short" LED to light up.
Now for the open circuit cable.
Assuming the open circuit cable has an infinite ohm.
Voltage divider near the dummy resistor will give 9V.
This is more than the upper "Comparator" limit (VRef 4.8V) and will trigger make "Open" LED light up.
Other than that (both lower and upper "Comparator" didn't trigger) the "GOOD" LED will light up.
For the op-amp, I'm using JRC4558 dual op-amp since I have it in my stock.
You may use 741 op-amp or other multi-purpose op-amp.
Learn more about op-amp here

Vref tuning

Before turning on the circuit (power it up),
tune the potentiometer so that it will give the correct voltage reference to the "Comparator"s.

• Upper "Comparator" = 4.8V


• Lower "Comparator" = 4.57V

Extra - Low battery indicator

The extra circuit supplied is to check the battery condition.
Low battery voltage (below than ~6.9V) will show "RED" light up.
Else will show "GREEN" LED light up.
The basic, if there is a small amount of current go through the zener (reverse bias),
the first transistor (left) will be turned on making the "GREEN" LED turn on.
Other than that the second transistor (right) will be turned on and "RED" LED will light up.

Modification - Add in buzzer

You add in buzzer to the circuit to make it give an audible alarm.
The best is to alert us whenever the cable under test is not "GOOD".
So, adding a resistor, transistor and a buzzer/beeper to the last NAND (near "GOOD" LED) will do the job.
Use your own creativity for this. :-).

Modification - Without NAND? (update)

You can use circuit above as replacement. Only some resistors and a transistor will do. Please refer to Water Level Indicator for more info.

Testing XLR cable (update)

Since XLR cable have 3 wires, it can be tested by connecting 2 wires at a time as image above. Use crocodile clip for easy access.

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Upgrading DivX Player Firmware

Upgrading DivX Player Firmware

Planning to upgrade your DivX player using CD? Good idea but if anything happen, your player will be dead.
In order to revive it, you need to re-flash it.



Refer here for more information about re-flashing your DivX player.


Upgrading a dead player - By DivXpert.




You can download some recommended softwares from their site and try it out.
Now the fun part, you need a hardware interface from your computer to the player.
Recommended hardware interface by DivXpert is standard Serial Data Cable for mobile phone.
So I built one.

Identifying The Upgrade Port

• Open up your player and find the main PCB & the upgrade port.


• Most of them have 4 pins [3.3V],[TX],[RX],[GND].


• Find the label for each pin under the PCB.

What You Need

• 
  I found out that the male audio input connector from the old sound card
  is suitable for the upgrade port. Use it if you have one.
  


• Old mouse cable match the female connector to this type of connector.


• Find a cheap mobile serial data cable/ I'm using Nokia 3210 data cable.

Install & Join It Together

• Open the data cable (phone end connector)


• Join it with the female mouse connector.


• Plug it into the player PCB and you are ready.


• 
  Refer
  "
  Upgrading a dead player - By DivXpert.
  "
  for detail.
  

My Other Version of Cable

• Another option is to find MAX232 chip from maxim.


• 
  
  Better if you have MAX3232 since this chip is using 3.3V
  
  


• I'm using normal MAX232 (5V) since I don't have one.


• Because of that, I need to connect the power of the MAX232 chip to the player +5V port

After that?

Please refer to
"
Upgrading a dead player - By DivXpert.
"
for the software usage on how to upgrade.
They provide the latest firmware for your Player.

Good Luck

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Biquad ant. for WLAN

Biquad Antenna for 2.4 GHz - 802.11b/g - WiFi - WLAN

After some research, I found out that the simplest type of
homemade WLAN antenna is BiQuad antenna. Many sites provide good
instruction on how to assemble it.

(refer below)

• "Biquad Antenna Construction" target="_blank">Biquad Antenna
  Construction


• "Biquad Sector antenna for 2.4 GHz" target="_blank">Biquad Sector
  antenna for 2.4 GHz


• "_blank" title=
  "Building a biquad antenna for wireless 802.11b">Building a biquad
  antenna for wireless 802.11b


• "Trevor Marshall BiQuad 802.11b Antenna">Trevor Marshall BiQuad
  802.11b Antenna [My favorite]

I'm not going to repeat it.

My Antenna

So I start by recycling some parts that I found in my workshop
and construct it.



I took about 10-20 min. for me to finished it.



The critical process is to make the element.

With proper method and dimension this thing will work.

Good Luck!!!

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ATX PSU Diagnose

About ATX Power Supply

ATX Power Supply converts the wall (AC) to the direct current (DC) needed by the
PC. The power supply looks like a metal box with fan.
Typical computer power supply generates the voltages needed by the computer motherboard accessories.
[Read more...]

Before Everything

Disconnect all socket from your main board, HDD, CD/DVD drive, Floppy drive and etc so that we can isolate which part
is not working.

Step 1 - Check Wall AC power

To check this, you may try to plug in any electrical appliances to the wall socket to verify that the 240V exist
such as lamp, table fan or etc. If it is working, that mean the power from the wall socket is ok.
You may also check the voltage with multimeter if you have one.

Step 2 - Power Socket Fuse

If you are using power socket with fuse, you may try to check this first.
The method is to plug the other end to other appliances such as your printer (turn on to verify),
monitor (turn on and look for LED indicator) or rice cooker (My rice cooker using the same type of socket).
Same thing, if it is ok, we know up to the power cord is also ok.

Step 3 - Voltage Selector

Not all power supply have this switch. My place using 240VAC.
So if it accidentally set to 110VAC the power supply maybe burn out. No more further troubleshooting.
But at place with 110VAC, maybe it will not burn out when it accidentally set to 240VAC.
It will in the low voltage condition and may not start I presume.
Select the correct voltage according to power provider rating.

Step 4 - 5V+ Standby Voltage

From bluemax.net







The first point that have voltage upon plug in the AC power is the standby voltage.[refer figure above]
5VSB constantly provides 5V power to the connector at pin 9.
Check this voltage using volt meter to make sure that 5V exist (while the AC is turn on).

Step 5 - Simulate Power On

Now is the interesting part. To turn on your ATX power supply without mother board, the way is to make contact
between pin 14 and ground pin(3,5,7,13,15,16,17). Meaning you can turn it on by connecting pin 14 with the only green wire
connecting to it to other ground pin that is the pin with black wire. To verify that the power supply is working,
the ventilation fan should be working split second after you connect pin 14 to ground. Paper clip would be the best choice.

Step 6 - Check All Output

Now you can check all voltage output from the power supply. You need a voltmeter in order to do that.

Pin Name   Color Description 1 3.3V   Orange +3.3 VDC 2 3.3V   Orange +3.3 VDC 3 COM   Black Ground 4 5V   Red +5 VDC 5 COM   Black Ground 6 5V   Red +5 VDC 7 COM   Black Ground 8 PWR_OK   Gray Power Ok (+5V & +3.3V is ok) 9 5VSB   Purple +5 VDC Standby Voltage (max 10mA) 10 12V   Yellow +12 VDC 11 3.3V   Orange +3.3 VDC 12 -12V   Blue -12 VDC 13 COM   Black Ground 14 /PS_ON   Green Power Supply On (active low) 15 COM   Black Ground 16 COM   Black Ground 17 COM   Black Ground 18 -5V   White -5 VDC 19 5V   Red +5 VDC 20 5V   Red +5 VDC From bluemax.net

Good Luck

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S/PDIF - TOSLINK interface

Circuit & Information on TOSLINK interface

So you want to get a high quality audio for minidisc recording but when
using red and white RCA, the quality drop drastically. Here a my cheap solution for you.
Actually you can find a lot of references of this type of simple project in the internet.



REF


* S/PDIF = Sony/Philips Digital Interface

* TOSLINK = (

TOSLINK Interconnect History & Basics

)

* Another web offering the same information


* SPDIF at epanorama.net







Meet my version of cheap, 2 components TOSLINK @ S/PDIF.
Try to find a cable with connector from old PC casing for this.
(HDD led,reset switch or power button connector)






Assemble it using your own creativity. Use the pen tube for the light transmission.






Connect it to the back of your CDROM drive. Since (D, the signal should go to anode and G should go to the ground/cathode)






Test it out. you should see the light come out from the tip/tube.







Connect to your MD or other device such as power amp that support optical in.






Actually, I have one of this (USB to SPDIF converter) for my minidisc but just to share with you on how to find a supercheap
solution before start buying. :-)


Even my new MSI mainboard do have built-in TOSLINK :-)

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