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palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805

Posted: 11:08pm 16 Oct 2013

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If anyone is interested Deal Extreme have EM-408 GPS for $15.40.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

kiiid

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Joined: 11/05/2013
Location: United Kingdom
Posts: 671

Posted: 11:27pm 16 Oct 2013

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I have one too, just happens to be on special right now. It is not as cheap, but is much more sensitive and comes on the next day

http://dimitech.com/?wpsc-product=dtx2-2800c

http://rittle.org

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palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805

Posted: 11:44pm 16 Oct 2013

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Just bought 2 from Deal Extreme but will buy one of these as well just to see how it performs. Have not heard of this company before, but I would rather buy from Australia if I can. Problem is the prices in Aust. are normally a bit over the top.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

donmck

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Joined: 09/06/2011
Location: Australia
Posts: 1310

Posted: 11:22am 17 Oct 2013

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I have a couple in stock on my Olimex 30% off deal. These are dearer also, but have the UEXT connector that matches the DuinoMite boards.

http://www.dontronics-shop.com/mod-gps-gps-sirf-star-iii-mod ule-with-internal-patch-antenna-2-meter-cable-and-uext-conne ctor.html

Don...

https://www.32v8.com/d

Geoffg

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Joined: 06/06/2011
Location: Australia
Posts: 3167

Posted: 04:12pm 17 Oct 2013

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Thanks, an EM-408 GPS for $15.40 is very cheap... I have bought a couple as spares.

There is an article describing a GPS Tracker for vehicles in the next issue of Silicon Chip and it can use the EM-408.

Geoff

Geoff Graham - http://geoffg.net

JohnS
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Joined: 18/11/2011
Location: United Kingdom
Posts: 3678

Posted: 12:53am 18 Oct 2013

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Good find - thanks!

John

paezle
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Joined: 11/03/2013
Location: Ecuador
Posts: 5

Posted: 05:57am 20 Oct 2013

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Hi!
I saw the GPS Module in DealExtreme and I want to buy one.
I have only a question about the connector and the antenna. Which type is the antenna connector, MMCX or SMA? It's necessary the antenna?
Thank you very much!!

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805

Posted: 11:47am 20 Oct 2013

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The antenna is MMCX and it is not normally needed. I have a clock working indoors under a metal roof with no problems.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805

Posted: 11:52am 20 Oct 2013

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DX also have an external antenna to suit for $6.00.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

paezle
Newbie

Joined: 11/03/2013
Location: Ecuador
Posts: 5

Posted: 01:03pm 20 Oct 2013

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Thank you very much Paul!!!!

paceman
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Joined: 07/10/2011
Location: Australia
Posts: 1329

Posted: 05:26pm 15 Nov 2013

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palcal said If anyone is interested Deal Extreme have EM-408 GPS for $15.40.
Paul.

Hi Paul,
How did you go with these? I got one in and assumed it would be communicating at the 3.3v "TTL" levels, i.e. 0v = logic 0, 3.3v = logic 1 and idle state at 0v. I fired it up connected to the Maximite's COM1 port and it's 3.3v supply but I can't get anything intelligible. It seems to be communicating, because I can see data coming in regularly every second or so using the program below - I used 4800 Baud because that's what the data sheet downloaded from DX.com said it used normally.

OPEN "COM1:4800" AS #1
do
x$ = input$(1,#1)
if x$ = "*" then Print
print x$;
loop
close #1
end

I checked back on the DX.com site and then noticed in the reviews of the module that the reviewers said it was operating as RS232. This tied in with 7v levels that I saw on the data when I checked it's output on my oscilloscope.

Any thoughts?

Greg

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805

Posted: 12:54pm 16 Nov 2013

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Greg,
Have a look at GPS in the Maximite library. That is the code I used and it works fine. Also look at EM-408 on Geoff's web site under General Articles.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

paceman
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Joined: 07/10/2011
Location: Australia
Posts: 1329

Posted: 12:58am 17 Nov 2013

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Hi Paul,
Yes I looked at Geoff's info and ran the library code but couldn't get anything intelligible - I'm wondering if I've got a dud but I want to be sure about the connections.

I connected as follows:

Linked pin 1 (grey) of EM 408 module (this should be the 'Enable' line), to pin 5 of the module (Vcc).
Pin 2 of module to Maximite Gnd.
Pin 3 (RxD) of module direct to MM pin 16 (COM1 Tx)
Pin 4 (TxD) of module direct to MM pin 15 (COM1 Rx)
Pin 5 (Vcc) of module direct to MM 3.3v.

Is this how you connected?

Greg

paceman
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Joined: 07/10/2011
Location: Australia
Posts: 1329

Posted: 03:12am 17 Nov 2013

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Paul,
I finally got it! The DX.com EM 408 module I have is definitely putting out RS232 levels; high at +7v, low at -7v and held high between transmissions. I wired it through a Max232 converter chip (actually Intersil HIN232 CP) that I had here and now it works! The strings come in fine with the following simple program on the Maximite.

OPEN "COM1:4800" AS #1
do
line input #1,x$
print x$
loop
close #1
end

I also ran Geoff's "GPS.com" code in the library and it extracts the Lat/Lon nicely.

Greg

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805

Posted: 12:11pm 17 Nov 2013

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Greg,
That's a bit odd, the data sheet says it puts out TTL level 0~2.85V. and I have two of them running without a converter. But I have not tried the latest ones I purchased from DX. Geoff also bought some maybe he can shed some light on this.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

Geoffg

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Joined: 06/06/2011
Location: Australia
Posts: 3167

Posted: 02:44pm 17 Nov 2013

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I dug out one of the modules from dx.com and I can confirm that there are two versions of the EM-408 with the same part number. The standard version uses TTL voltage levels on its serial output (idle is 2.7V, the start bit and logic 0 are zero volts). The alternative from dx.com uses RS-232 voltage levels and polarity (idle is -6.8V, the start bit and logic 0 are +6.8V).

Thanks are due to Greg and his detective work in discovering this.

The only way that you can tell the difference is by physically looking at the module. The TTL version has the shield extended over the connector as shown in this photo:

The RS-232 version does not have this feature as shown in this photo:

The documentation only refers to the TTL version and when you are ordering one of these modules you have no assurance of what one you are going to receive as the part numbers (EM-408) are the same.

It is incredible that a manufacturer would create such confusion in the market place and unfortunately their crime is compounded by the dreadful documentation that they supply.

Geoff

Geoff Graham - http://geoffg.net

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805

Posted: 03:09pm 17 Nov 2013

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According to the Globalsat web site this version is EM-408E and it says it has USB interface connection port but then further on it says "GPS-TX Output TTL level, 0V ~ 2.85V". Anyway we now know how to use it thanks to Greg.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

JohnS
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Joined: 18/11/2011
Location: United Kingdom
Posts: 3678

Posted: 03:24am 18 Nov 2013

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Geoff - thanks for the info!

pah - seems I have the non-TTL one, most likely. Just arrived.

Markings:
anti-static bag: 234188 & barcode 00034023631
sticky white label on device: 306774

JohnEdited by JohnS 2013-11-19

Geoffg

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Joined: 06/06/2011
Location: Australia
Posts: 3167

Posted: 04:54am 18 Nov 2013

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JohnS said Markings:
anti-static bag: 234188 & barcode 00034023631

Yep, that is the RS-232 version.

Geoff

Geoff Graham - http://geoffg.net

paceman
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Joined: 07/10/2011
Location: Australia
Posts: 1329

Posted: 02:54pm 18 Nov 2013

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The markings on my RS232 version from DX.com are a bit different:

Anti-static bag: 234188 & 34023647
White stick-on on the module: 310490

Using the Max232 type converters is straight forward but they do need five support 1uF electrolytics and typically they use a 5v supply - this bulks things up a bit. Mine looks like below:

The 'generic' I used (Intersil HIN232 CP) says 0.1 or 1.0uF caps can be used but they need to be polarized. I'm not sure whether tantalums would also be OK but if they are then the bulk could be minimized - along with using an SMD version of the 232's.

Prices for the DIP16 version of the converter chips I've seen are:

Rockby - $1.95 (MAX232CPE)
Jaycar - $4.95
Element14 - $2.07 (MAX232CPE+)
Futurlec - 1.50 (MAX232CPE)

Guess at DX's price of $15 it still makes for a cheap EM 408 option but for us it's obviously better to get the 'TTL' version.

Greg

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