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Got a technical problem? Can't understand a piece of jargon or some technical principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097 or send an email to silicon@siliconchip.com.au

Dual voltage version
of charger

I am considering building the battery charge controller from the April 2008 issue of SILICON CHIP. I was wondering if it is possible to make it dual voltage (ie, 12V & 24V) or do you have a dual-voltage version in mind? Most most commercially available chargers are mainly one or the other. (J. G., via email).

• Yes it is possible to make the controller dual-voltage. Resistor R1 should be switched in value to 51kΩ for the 24V version. Use a 150Ω 0.5W resistor for the feed resistor from diode D1 to the 24V zener diode ZD1.

These can be switched using a double pole double throw (DPDT) switch to change between the 12V and 24V settings.

Dimmer touch plate needs cleaning

I have built the Touch/Infrared Dimmer project (SILICON CHIP, January & February 2002) and have problems with the touch plate input constantly triggering. I have carefully checked my work and have 5V at the micro. The dimmer does work if I remove the touch plate and touch only the contact screw. Any help would be appreciated. (D. W., via email).

• The plastic plate requires cleaning. Remove the touch plate and wipe the plastic plate with a cloth to remove any film or residue that may be present. Any coating on the plastic will conduct and cause the dimmer to constantly cycle on and off in a similar way to if a hand is held on the touch plate.

Regular cleaning is necessary to keep the plate clean.

Router ignores
the WIB

I completed construction of the WIB kit (SILICON CHIP, November & December 2009, January 2010) and would like to say that it is an excellent project and quite straightforward to build. I set it up as per the instructions and it works perfectly. It is connected to my home network and accessible from my web browser, however it is not recognised in the list on my network router.

My ISP is Bigpond and the modem/router is a 2-wire ADSL gateway. Any other device shows up on the list when I connect it to the router. The router has four LAN Ports and wireless, with two ports connected and three wireless laptops. All are recognised except for the WIB.

My question is, should the router
table include the WIB when connected? (J. C., Branxholm, Tas).

• Depending on your router, it may show up or not. For some routers, it will not show up if the WIB is set up to use a static IP address – which is the way we have recommended in the magazine article. It may be that your router is only showing the devices that use DHCP. Therefore, it makes sense that the WIB is not showing up because we have recommended a fixed IP address.

Reducing The Battery Shutdown Threshold For Ultrasonic Anti-Fouling

I have purchased two Ultrasonic Anti-Fouling kits (SILICON CHIP, September & November 2010) and would appreciate your recommendation on changing the battery monitoring circuit to an 11V cut-out instead of 11.5V. The reason for this is that if other high-current accessories in the boat are drawing power and say, the electric toilet is flushed (along with the slight voltage drop on the 10-metre cables to the transducer drivers), the 11.5V threshold may be breached. (B. W., McMahons Point, NSW).

• Low voltage shut-down occurs when the voltage at pin 5 of the microcontroller is below 3.833V and operation is restored at above 4V. With the 20kΩ and 10kΩ divider resistors that are used to reduce the battery voltage, 3.833V is reached at pin 5 when the battery voltage is 11.5V. Similarly, operation is restored at a battery voltage of 12V.

The resistive divider can be altered to change the low-voltage shut-down For an 11V shut-down, the 20kΩ resistor at pin 5 is reduced to 18.857kΩ by placing a 330kΩ resistor in parallel with it. Operation will be now be restored when the battery voltage is 11.54V.

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