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Ask Silicon Chip

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

GPS Car Computer enhancements

I am writing in relation to the GPS Car Computer featured in the January 2010 issue. Unless I have missed something in the article, it appears that the basic “GPS Car Computer” has no on-board memory in which to store collected data for later analysis on a desktop PC via the USB port. The article seems to suggest that a laptop computer has to be connected to the GPS-CC when the vehicle is being driven in order to be of any value.

So my question is could a future project be designed that adds a non-volatile memory component to this very useful device and software provided for installing on any PC, so that a full trip profile can be obtained at the conclusion of the trip? In the interest of road safety it would obviously be impractical to use the device connected to a laptop if the driver were to be the sole occupant of the vehicle. It could only be used in this configuration when there is a passenger and as such, couldn’t be used as a satnav replacement at all times.

Although the GPS-CC device is obviously not a replacement for the “Davis Instruments CarChip”, a version of which was reviewed in SILICON CHIP sometime ago, the DICC does allow for data to be downloaded at the completion of a journey for later analysis. (P. M., Karabar, NSW).

• We put your questions to the designer, Geoffrey Graham and this is his reply:

You certainly have a high level of requirements! Regarding tracking a journey: it could be done but it would take a redesign, the main difference being that a microcontroller with much more flash memory would be required.

This type of chip is cheap enough but they are mostly only available in surface-mount TQFP packages with 0.2mm between the pins (three times the width of a human hair!). They can be soldered (I have done it) but you do need to be adventurous and prepared to ruin a chip or board or two.

Also, you are right. It is not a replacement for the “Davis Instruments CarChip”. That was a completely different beast and much, much more complex.

Fuel mixture display needs air-flow input

I purchased a Smart Fuel Mixture Display kit (SILICON CHIP, April 2004). On installing it into the original set-up in car with an oxygen sensor and air-flow meter all works fine. My problem arose when I removed the air-flow meter, due to fitting a set of throttle bodies which have no air-flow meter. Is it possible to use the throttle position sensor instead of the air-flow meter? (J. W., via email).

• As the name suggests, “throttle position sensor” indicates throttle position rather than engine load. However, it could be used instead of the air-flow meter with the understanding that the throttle position does not always match the engine load, especially in low gear.

Upgrading The 12V Battery Charge Controller

I have just read a reply in “Ask SILICON CHIP” for May 2010 about a 24V modification for the 12V Battery Charge Controller published in the April 2008 issue. It occurred to me that this could possibly solve my problem with a 48V golf-cart charging system.

The bank has six 8V Trojan T-875 wet cell, deep-cycle batteries which I am charging with a standard 48V centre-tap transformer/twin-diode type charger. However, I would like to upgrade it to the battery charge controller system.

Would this be possible? As far as I can determine the RC for these batteries is 295 (295 minutes @ 25A), or a 125Ah rating. My charger supplies up to 20A on start up.

If what I ask is not viable can you suggest an alternative or, better still, can you describe a golf cart charger with dual voltage 36V and 48V outputs? (J. N., Mt. Maunganui, NZ).

• The 24V modification for the float charger as described in the May 2010 issue was for the March 2003 charger. However, the April 2008 charger design could be modified for 36V and 48V.

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