Simple J-Tag Construction Question

[Joe_4090]

Good Morning All:

I am in the process of building a simple J-Tag
as per the guide which I downloaded else-
where on this forum. I decided to stop and
check a couple of things before proceeding
further:

Question 1. Does it matter how the resistors
are positioned? The guide showed them with
the brown/black/brown bands facing upwards
toward the head of the connector....but I in-
advertently soldered a couple of them with
the bands facing downward. Does this matter??

Question 2. Radio Shack was out of the 100 ohm
1/4 watt resistors which the guide called for. The
clerk gave me some 1/2 watt ones...saying they
would make no difference. Is he correct, or should
I go back and find 1/4 watt ones??

Question 3. R/S also didn't have any 6-wire ribbon
cable. I cannibalized some different colored wires
from an old computer part...but these are thicker
than ribbon cable wires. Would this make a differ-
ence or should I use smaller gauge wires??

Thanks for any input.

[BiggerBear]

It doesn't matter how the resistors
are positioned.
You need to get 1/4 watt. Don't believe those clerks - follow the specs.
I used regular 6 conducter phone wire and the phone jack on the back of the receiver (had to cut traces on the board) from the phone jack to the Jtag Pads I used 14 guage wire I had laying around and it works great

[Joe_4090]

Thank you, BiggerBear....much appreciated.

Oh dear, back to the drawing board! :)

[Joe_4090]

Thank You Racer88

[BiggerBear]

When the 1/2 watt resistors don't work be sure and let "Racer88" know.
I have seen this myself - the 1/2 watt don't work.

[Joe_4090]

Uh Oh......bad news...............
IT DOESN'T WORK!!
I checked everything....looks good. I don't know if the
wires are too thick, or too long (17")...or wrong resistors.....
but I tried everything I could think of and.....nada.
I'm not saying anyone's info was bad...it might be some-
thing I did. I'm just saying I can't get it to work.

Good news is, I got my original buffered one from Mili to
working again!

(Slinks into a corner with popcorn and beer to watch en-
suing fight!! :) )

[BiggerBear]

I told you it wouldn't work with the 1/2 watt resisters.

[skinerd]

When the 1/2 watt resistors don't work be sure and let "Racer88" know.
I have seen this myself - the 1/2 watt don't work.

There is absolutely no reason the 1/2 watt resistors won't work in place of 1/4 watt.

They are of the same resistance, and that's all that matters.
Wattage is a measure of how much power they can dissapate, which is not a concern when going to a larger wattage. Even 1/8 or 1 watt would work, 1/8 is a little to delicate, 1 watt is big, physically, but they would function perfectly.

[skinerd]

Uh Oh......bad news...............
IT DOESN'T WORK!!
I checked everything....looks good. I don't know if the
wires are too thick, or too long (17")...or wrong resistors.....
but I tried everything I could think of and.....nada.
I'm not saying anyone's info was bad...it might be some-
thing I did. I'm just saying I can't get it to work.

Good news is, I got my original buffered one from Mili to
working again!

(Slinks into a corner with popcorn and beer to watch en-
suing fight!! :) )

Some PC/parallel ports don't like the unbuffered jtags.
Wire size is no issue, length maybe, 17 inches is way too long..
The only issue with large wire is getting it connected without shorting to the next closest connection or ground.
Some people just have no sucess with non-buffered jtags, and it is generally a PC or parallel port issue.

[STAGEBUM]

I have a Universal DUAL BATTERY Powered & BUFFERED JTAG from Dsshouse.com had no luck getting it to read basically does not detect my 3900 which is all I have to test on checked all my settings hooked in to 1lpt jkeys set to parallel port which is were i hooked my jtag to "printer port" one question is what is Jinterface settings for when i try them tells me coms dont exist exept when i try com 3 tells me it failed because some other device is using it so I am totall lost at what to do. What sould my bios settings be and my jkeys set at? I have xp dell 4800c pc. Please can someone give me some advise.

Thank you so much
Stagebum

[Westy]

I made mine from a parallel port cable out of a computer case, no resistors and topside connection like the Odd Circuits design. I routed it out the back of my 4700 receiver and have access to it with the top on.

It has worked well for me so far. I might spring for some resistors, but as of yet I don't see a need for them. It reads and writes on the first try every time


------------
Westy

[Joe_4090]

Thank you Skinerd:

I will tinker with it some more later. Try shorter
and smaller wires. If it still doesn't work...then
you are probably right about the unbuffered j-
tag/parallel port issue.

[skinerd]

I made mine from a parallel port cable out of a computer case, no resistors and topside connection like the Odd Circuits design. I routed it out the back of my 4700 receiver and have access to it with the top on.

It has worked well for me so far. I might spring for some resistors, but as of yet I don't see a need for them. It reads and writes on the first try every time


------------
Westy

I wish you continued good luck.
The parallel port is 5v and the IRD 3.3v, directly connecting them without current limiting resistors is only asking for problems. Which you may or may not experience, but why take the chance to save $0.15????

[DSSNobody]

Hi,

Just some information ( I don't post much, but I do post when I have expert information available ).

I have recently used the scematics to create 7 phone jack JTAGS (schematics available for download here at Mili's site).

Please note the following:

1). You can use either the 1/4 watt or the 1/2 watt 100 ohm resistors. I have found that the 1/4 watt work better ONLY because they are smaller and fit into the connector shells better.

2). I have successfully made the phone jack JTAGS up to 3 feet long using standard 24 gauge 6 wire phone cords from Radio Shack.

3). PLEASE USE THE RESISTORS. You can screw your IRD without them.

4). Please read and follow #3 (can't stress this enough) ... you already know it works and you have the wires setup correctly. Please interrupt them and place a resistor on all but the ground.

5). Cost for the phone jack JTAG:

$5.99 - 6ft 6 wire phone line (with ends terminated to RJ11)
$1.49 - D-Shell connector kit (holds the 25 pin d connector)
$1.29 - D-Connector 25pin
$0.99 - 5 100 OHM 1/4 or 1/2 watt resistor pack

You can make 2 phone jack JTAGS for under $10.00 ... and sell one to make up the entire cost of the project.

=) ... always make your JTAG as short as possible ... my 3 footers DO work but they have been doing it longer than me. I only JTAG to 2700, 3700 and 301 so my 3 footer may not work with other IRDs. I would follow their advice and make it as short as possible (I did 3 footers so I could just set my laptop on the top of the TV stand and reprogram).

[Westy]

See now that's why this site is so great. Now that I know the reason for the resistors I will install them.

[DSSNobody]

LMAO gotta love debates between ppl that have ABSOLUTELY no understanding of how electronic parts actually work LMAO

Even the ratshack flunky knew that much suprisingly ROFL

LMAO gotta love debates between ppl that have ABSOLUTELY no understanding of how electronic parts actually work LMAO

Even the ratshack flunky knew that much suprisingly ROFL


I think you are confusing the OHMs rating with the wattage rating.

When a current is passed through a resistor, heat is developed within the resistor. The resistor must be capable of dissipating this heat into the surrounding air; otherwise, the temperature of the resistor rises causing a change in resistance, or possibly causing the resistor to burn out. The ability of the resistor to dissipate heat depends upon the design of the resistor itself. This ability to dissipate heat depends on the amount of surface area which is exposed to the air. A resistor designed to dissipate a large amount of heat must therefore have a large physical size. The heat dissipating capability of a resistor is measured in WATTS. Some of the more common wattage ratings of carbon resistors are: one-eighth watt, one-fourth watt, one-half watt, one watt, and two watts.

The higher the wattage rating of the resistor the larger is the physical size. The larger the physical size the more effective it dissipates heat.

A 1/2 watt resistor of 100ohms will work in place of a 1/4 watt resistor of 100ohms.

[Crazy1_79]

Good Morning All:

I am in the process of building a simple J-Tag
as per the guide which I downloaded else-
where on this forum. I decided to stop and
check a couple of things before proceeding
further:

Question 1. Does it matter how the resistors
are positioned? The guide showed them with
the brown/black/brown bands facing upwards
toward the head of the connector....but I in-
advertently soldered a couple of them with
the bands facing downward. Does this matter??

Question 2. Radio Shack was out of the 100 ohm
1/4 watt resistors which the guide called for. The
clerk gave me some 1/2 watt ones...saying they
would make no difference. Is he correct, or should
I go back and find 1/4 watt ones??

Question 3. R/S also didn't have any 6-wire ribbon
cable. I cannibalized some different colored wires
from an old computer part...but these are thicker
than ribbon cable wires. Would this make a differ-
ence or should I use smaller gauge wires??

Thanks for any input.
I used half watt and the banded end of the resistor is suppose to be towards the 25 pin connector, The wattage is merely the Maximum watts the resistor can handle, a little over the wattage is ok, you just never want to go under what is recomended, If you have the resitors backwards I don't know if it will work or not. I put all of mine on the right way

[skinerd]

I used half watt and the banded end of the resistor is suppose to be towards the 25 pin connector, The wattage is merely the Maximum watts the resistor can handle, a little over the wattage is ok, you just never want to go under what is recomended, If you have the resitors backwards I don't know if it will work or not. I put all of mine on the right way


Ther is no wrong way for a resistor...........it don't matter which way goes where, you can't install one backwards...............

[Crazy1_79]

Ther is no wrong way for a resistor...........it don't matter which way goes where, you can't install one backwards...............
Thanks skinerd, I wasn't sure about resistors, I knew capacitors have to go in a certain way. LOL, care to guess how I learned that one?? *BANG* I was young and have no electronics training whatsoever just learned what I know on my own

[samantonio23]

Hello, I'm a Electronics Enginner
And:

-Resistors doesn't have polarity, so you can put them in the position you want.
Only for reading color code(to know resistor value) position matters.
- Watts, as Crazy1_79, just worrie if you put a resistor with a lower watt.
So 1/2 should and must work.

[2canoe]

If I may refer you all to one of many sites. easy way to ID resisters. automatic chart to decode resistor values, now you can save a few pennys and rob resistors out of old circut boards, Works good for those that like recycling.
http://www.csgnetwork.com/resistcolcalc.html
thanks