Newbie questions

[Cameron McCormack]

Hi.

I'm a bit of an electronics newbie. I did a year of digital electronics
subjects back in first year uni and a semester of analog.

I have a Navman (Connexant) Jupter 10 GPS module [1] that I want to
connect to the serial port of my computer. There are a few things
though that I need to get sorted before I can do this.

1. The connector on the board is a "dual row, straight 2x10 pin field
connector header. The pins are spaced on 2.0mm centers...". I went to
Jaycar and Radio Parts today to try to find a header socket that would
fit these pins, but they only had some IDC ones which are too big.
Where could I get an appropriate connector?

2. The serial I/O from the board is TTL, and I gather that the serial
port of my computer uses CMOS levels. Googling around I found this page
[2] which says I need a MAX232 or DS275 chip to do this. I guess the
DS275 is preferable, not needing the capacitors. Where can I get one of
these?

3. I am wondering what to use as a power source to this thing, both
during development and when I eventually put it in a box. I don't have
a power pack that can generate me a nice 5V. I'm wary of using a plain
old transformer that you plug into the mains in case I short the circuit
or something and trip the fuses in the house. Should I just get a
couple of batteries and a voltage divider from a couple of resistors?
Is there a way I can get the batteries to stay within the strict power
requirements of my GPS board (5V +/- 0.25V)?

Thanks for your help,

Cameron

[1] http://mcc.id.au/~cam/Jupiter%2010%20Datasheets.pdf
[2] http://chaokhun.kmitl.ac.th/~kswichit/MAX232/MAX232.htm

--
Cameron McCormack
| Web: http://mcc.id.au/
| ICQ: 26955922

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[Ken Taylor]

"Cameron McCormack" <cam-news@aka.mcc.id.au> wrote in message
news:403de73b$0$27644$61ce578d@news.syd.swiftdsl.com.au...

Hi.

I'm a bit of an electronics newbie. I did a year of digital electronics
subjects back in first year uni and a semester of analog.

I have a Navman (Connexant) Jupter 10 GPS module [1] that I want to
connect to the serial port of my computer. There are a few things
though that I need to get sorted before I can do this.

1. The connector on the board is a "dual row, straight 2x10 pin field
connector header. The pins are spaced on 2.0mm centers...". I went to
Jaycar and Radio Parts today to try to find a header socket that would
fit these pins, but they only had some IDC ones which are too big.
Where could I get an appropriate connector?

Try Connect Electronics (in Melbourne, maybe elsewhere). Molex make a

suitable connector but I don't have their number. You can search at the
Molex website for wire-to-board connectors and search from there, but it may
be easier just to ring and ask.

2. The serial I/O from the board is TTL, and I gather that the serial
port of my computer uses CMOS levels. Googling around I found this page
[2] which says I need a MAX232 or DS275 chip to do this. I guess the
DS275 is preferable, not needing the capacitors. Where can I get one of
these?

The PC serial port uses RS-232, not CMOS. However you do need to interface
with a suitable chip, such as the MAX232, which you can get from Dick Smith
or Jaycar. Check their cattle-dogs for a suitable chip. Capacitors are
easy - go for it!

3. I am wondering what to use as a power source to this thing, both
during development and when I eventually put it in a box. I don't have
a power pack that can generate me a nice 5V. I'm wary of using a plain
old transformer that you plug into the mains in case I short the circuit
or something and trip the fuses in the house. Should I just get a
couple of batteries and a voltage divider from a couple of resistors?
Is there a way I can get the batteries to stay within the strict power
requirements of my GPS board (5V +/- 0.25V)?

Use a plug-pack, it'll be easier in the long run, and safer than messing
about with a transformer till you get some confidence up. Get one with about
9V at whatever current rating you'll require, and get a power diode, a 7805
regulator IC and some more of those nice capacitors from Tricky Dicky or
Jaycar. The diode is for reverse-voltage protection, so in case you put the
volts on back-to-front you don't destroy anything. I think the catalogs have
sufficient information for you to make up a circuit.

Thanks for your help,

Cameron

Have fun!

Ken

 

[Cameron McCormack]

Ken Taylor wrote:

Use a plug-pack, it'll be easier in the long run, and safer than messing
about with a transformer till you get some confidence up. Get one with about
9V at whatever current rating you'll require, and get a power diode, a 7805
regulator IC and some more of those nice capacitors from Tricky Dicky or
Jaycar. The diode is for reverse-voltage protection, so in case you put the
volts on back-to-front you don't destroy anything. I think the catalogs have
sufficient information for you to make up a circuit.

Cool, ok. That regulator looks good, so I can eventually just use a 9N
battery and it handles getting it to 5V. Reading some web pages with
circuits for this sort of thing, they say that for more than about 150mA
you should put a heatsink on the regulator. My GPS board needs a
maximum of 230mA. How should I affix the heatsink on to the regulator,
just with the same sort of paste I'd use to put fan/heatsinks on CPUs?

Thanks again,

Cameron

--
Cameron McCormack
| Web: http://mcc.id.au/
| ICQ: 26955922

Replies by e-mail must include the current month name in subject line to
bypass spam filter.

 

[Cameron McCormack]

Ken Taylor wrote:

and get a power diode

By the way, is the term "power diode" anything special? Or do you just
mean any old diode (that can handle the current/voltage) that is
connected between the power supply and the other components?

--
Cameron McCormack
| Web: http://mcc.id.au/
| ICQ: 26955922

Replies by e-mail must include the current month name in subject line to
bypass spam filter.

 

[Ken Taylor]

"Cameron McCormack" <cam-news@aka.mcc.id.au> wrote in message
news:403e9659$0$27645$61ce578d@news.syd.swiftdsl.com.au...

Ken Taylor wrote:
and get a power diode

By the way, is the term "power diode" anything special? Or do you just
mean any old diode (that can handle the current/voltage) that is
connected between the power supply and the other components?

--
Cameron McCormack

A heatsink can be a bit of metal; with 4V being dropped across the regulator
at 250mA (roughly - it makes the maths easy) that's only 1 Watt. Using some
heatsink compound will help.

Use something like a 1N4001 diode, rather than a signal diode like a 1N914A.
Both useful, but not interchangeable. Note that you should have a
capacitor, say 1uF, at both the input and output pins of the regulator. I'd
seriously look at a plug-pack, your battery won't last long with that
current draw, and a regulator like we're talking about is simple, but
wasteful. I'd recommend against a switch-mode plug-pack or regulator at this
stage as the switcher may cause some interference with your GPS module. Once
you know it works okay, then you can look at fancy stuff if you're
interested.

Cheers.

Ken