Sensing and Control for hobbyists and schools: Weather, Dallas 1-Wire Hub: Building it.

The bad news: The device most of this page is about is not always available. You may be able to find one second hand, though, or perhaps a bare pcb which you can populate yourself if you go to the trouble of ordering the various parts. The board is 14x4cm. It is marked "iButton 1-Wire Hub Simat ver 3". It is also marked with the following URL. It is worth a visit!
http://www.simat.org.uk: Site of designer, Simon Atkin .

I HAVEN'T BUILT THE THING YET!!!... but maybe you'll still find something of interest! Throughout, I talk as if I have constructed the kit because this page derives from one about building the barometer, which I have finished! (And, of course, one day I will get the hub built!) I am quite confident that everything here is correct EXCEPT I've yet to confirm the thought that you can leave incorporating D9-15 and D16-22 until the end... though I'm fairly confident about even that.

In the first half of 2002, the Dallas Weatherlist people did a group project which resulted in a kit of parts to build Simon Atkin's 1-Wire hub. Sadly, the discussion group is no more. Click here for information on it and alternatives.

If you have a kit of parts, or a second hand unit, you may be looking for someone to assemble, fix, or calibrate it for you. Click here for a list of willing folks.

The rest of this is some notes of things that I had to be careful about when assembling my own kit, just in case it makes things easier for you. You should view this as secondary to the excellent advice posted by Simon Atkin. You might want to download at least the schematic. Don't be confused by the LED pairs D3/4, D5/6, D7/8. Simon was showing that the pcb can accept two diodes in those locations: Either an SMD LED or an old fashioned one. You've been provided with the old fashioned sort.

Thomas Nolan has kindly done a photo of a completed hub for you. N.B.: He assembled his hub with some diodes (PK6E7.5A) lying flat. The board was designed assuming you'll put them upright. Getting them to fit flat might be difficult.

Many of the parts are extremely tiny. A clear workspace and a tray to work in are very good ideas. I also had a smaller tray (4" x 6") in which parts could live until required.

Start by printing out the parts list, if one's available. Otherwise generate one from the schematic as you go along with identifying your parts. Cut a piece of paper to fit the bottom of your small tray. Draw a grid on it with columns 4 cm wide. Label them A, B, C... etc. Make three 2cm high rows, and split the rest of your height into two more (larger) rows. Label the rows 1 - 5. Pour (carefully!) the contents of your pink bag into a pile in the middle of your big tray. Be sure there are no parts hiding in the sockets of the RJ-45 connector. Pick out the big bits, put them back in the bag. Pick up a small bit at random, identify it, put it in a square, and write the square's reference (e.g. A1) next to the part's entry on the parts list. Do this for all of your parts. You should find a part for each thing on the parts list.

By going through identifying everything first, you'll be more confident you're right if you think something's missing, and there's less chance of substituting one part for another. Get all of your identification issues resolved before you start assembly.

Most of the parts have numbers you can use to identify them. There are usually multiple instances of a given component type, I've given the number in brackets in my list below. Put all of them in a single cell of your parts tray. What you see on yours may vary from the following, but just in case what I had helps....
C2, C3: the "big" cans marked 33/ 25S/ 1N6
D16-22: the "large", traditional diodes: a cylinder with wires out the ends.
U1: Big thing with three legs, marked 7805
D9-D15: The little guys with 3 legs, of which you have 7. (There are two diodes in each package)
D1, D2: 3x5mm
U2,3,4: DS2409
R1,2,3,4: Tiny. Marked 391
C1,4,5,6: Similar to R1. Unmarked. Mustard color.
That's not everything, but I hope it covers the hard-to-identify.

Some components can be inserted either way 'round. Those that cannot will (I hope!) be mentioned explicitly in what follows. Components which must be inserted the right way 'round are called "polarized".

This would seem to be a spot for a big "thank you" to Alan, et al, for making no assumptions about our junk boxes and including an led and the header pins and jumpers, just in case. (Oh yes... and A case!)

I like to put an ohmmeter on the bare board before starting. Might as well find, fix flaws if they show up before the confusion of the components. There are many test you could make, but I'd suggest the following. All references to the board will assume that you have it turned so that the long dimension runs left and right and the pads for U1 are at the edge far from you which I'll call the "top" edge. All of the following should show open circuits...

-- Pads for C3, upper right.
-- The middle two pads in each of the RJ-45 connector pad sets. (by "middle two", I mean second pad from left in top row, second from right in bottom row.)
-- The two pads for each of D16-D22
-- To your patience's limit: See that there's no connection between the two pads for any one resistor or capacitor.

Solder in the resistors and small capacitors. Note that R1, R2 and R3 go left-right above their IDs. The pads below those IDs are for SMD LEDs if you want to install them instead of using the alternate holes just to the right of each pair of SMD pads. None of these small resistors or capacitors is polarized.

My thanks go to Jim Montague and brother for their sanity saving idea:

Take a stout pin or small nail. Take some Vise-Grips (aka Mole-grip) pliers... or a pair of needlenose pliers with a stout elastic band around the handles.... and grip the pin in the jaws of the pliers, at right angles to the jaws, with about 2" protruding. Find a book or something else solid that is about 2" high. Put it on your workbench, a little farther from you than your soldering area. Rest the handles of the pliers on the book so that the pin is pointing down. When you are ready to solder something, put the pcb under the pin. Put the component in place. Lift the pin, move it, lower it down on the component so that the weight of the pliers holds it in place. (It helps if you date back to the era of putting a needle on a vinyl LP record!!)

Obviously, you can modify the suggested arrangements to suit what you have to hand, but something like it IS a great help. A fine tip on your soldering iron is nearly essential. There's a good guide to soldering at EPE magazine's site.

At this stage, the pads for C3 should still show an open circuit, though it might not show that until your ohmmeter has been in place for a moment or two. (The capacitors will cause some current flow until they charge.)

Solder in the two big capacitors, C2 and C3. They ARE polarized. The silkscreen shows you which way they go.

Solder in D1 and D2. They ARE polarized. The band on D1 needs to point left, i.e. away from J2. The band on D2 needs to go up, i.e. away from J3.

If you do the resistance test now, say between the right hand pads for U1, you may see a short when the tester is attached one way 'round. You should still see an open circuit (after the capacitors charge) when the tester is attached the other way 'round.

Solder U1 in. It is polarized, the side with the large area of exposed metal goes to the outside, i.e. away from C2. When soldering in things with leads which pass through the pcb, be careful: sometimes, the lead is intended to connect to the broad area of copper on the back, which is called a groundplane. In other cases, the lead is NOT supposed to connect to the groundplane. The little gap around the place the lead comes through is not large, and care is needed.

Now you need to provide the board with some power. It needs to be 7-25 volts DC, doesn't need to be regulated. I'd go for 12v if you have it easily available.

Eventually, you may elect to supply the power via the RJ-45s. For now, wire it in via CN2, either y using the connector/ socket pair provided, or y soldering wires directly to the pcb.

The positive connection goes to the upper pin of CN2, i.e. the one near C1. The other two connections are connected to each other, either can be used for the zero volt connection to the power. After power is applied, you should see 5 volts between the pads for D3. (N.B.: This may be marked D24 on the schematic you have. It is NOT the partner of D4. It IS the LED connected to R4. The pad connected to R4 should be the positive pad.

With the power on, dry fit the green LED in D3, either way 'round. If it doesn't light, try it the other way 'round... no harm will have been done. It should light now, if it didn't before. You can remove the power and solder it in now if you want to. I'd e inclined to wait, because how long the leads should be left will e affected by casing issues.

Fit the header pins for JP1- JP7. Don't fit any jumpers yet.

This next check (down to "===") isn't essential if you want to skip it.

At each of the positions for DS2409s, i.e. at U2,3 and 4, the pad for pin 1 is at the upper left, i.e. for U2 pin 1's pad is just below the silkscreened "C4".

Apply power. Measure the voltage between the pad for pin 1 and the pad for pin 6. (They're numbered around the chip, anti clockwise, so pin 6 is the one at the upper right.) You should see 5v, with pin 6 being the positive side.

Look for voltages between pin 1 and each of the other pads. You shouldn't see any.

Remove the power, if you have it connected.

Solder in U2. The little dimple on the chip is beside pin 1.

At this stage, we need to be able to attach the hub to a 1-Wire net. You can connect two wires directly to the center two holes provided for the left hand (near CN2) RJ-45. The upper one is for the 1-Wire data, the lower one is ground. Alternatively, solder the block of RJ-45 sockets onto the pcb, putting it on the same side of the pcb as the components already soldered in place. BE AWARE: If you plug a cable in via the RJ-45, the outside two pins on the left are shorted and the signal on them taken to the right hand side of J4. The two pins on the right are shorted, and connected to the pcb's groundplane, itself connected to the zero volts side of the power supply.

Anyway... one way or another... connect your pcb with it's DS2409, and powered, to a 1-Wire LAN connected to a PC running the iButton Viewer program. It should show the presence of the DS2409.

Now... an admission... I don't know a lot about the hubs! In my limited and possibly inaccurate understanding, I think the DS2409 is essentially a switch. Pin 2 is connected to a 1-Wire LAN. Two further 1-Wire "sub-LANs" are connected to pins 3 and 4. I think that once you have the DS2409 up and running, you're able to connect either the sub-LAN connected to pin 3, or the sub-LAN connected to pin 4 to the "higher" part of the LAN, the one that feeds into the DS2409 via pin 1. This switching is accomplished via commands sent to the chip over the 1-Wire LAN. The iButton Viewer allows you to switch the switch (I would guess!)

Besides the three important connections mentioned above, there's an output to allow you to see which way the switch is standing without being "inside" the LAN. This signal is an output on pin 5 of the DS2409. It is connected to D4 in the pcb. Switch things one way, and, if you insert an LED in the pads at D4 (the right way 'round... and it is safe to try it both ways), the LED will glow. Switch things the other way and D4 will go off.

That overview oversimplifies the functions of the DS2409, but it should suffice for assembly and checking.

If the iButton Viewer is showing the DS2409, you can try the following. You still don't need to connect jumpers to the headers. Their role is something for another time, if you can't get what you want from Simon's site, where I have no doubt they are explained, though I haven't looked. (yet!)

For the following, the RJ-45 sockets are numbered as follows: The one nearest CN2 I am going to call "1". The next to the right is "2" and so on.

Before embarking on the following, remember what I said above about what is connected to the outside two pins (each side, 4 in all) of each RJ-45 socket.

Plug some 1-Wire device into socket "3", and another into socket "4".

The iButton Viewer ought to "see" one of the devices you plugged in. When you switch the DS2409, the thing you "saw" before should disappear, and the other thing plugged in should appear.

Assuming all's well, solder in U3. Once it is in, don't change your connection to socket "1", but move the devices in sockets 3 & 4 to sockets 5 & 6.

Assuming all's well, solder in U4. Once it is in, don't change your connection to socket "1", but move the devices in sockets 5 & 6 to sockets 7 & 8.

Once things are working for you, install diodes D16-D22. The band on the diode goes to the left, as shown on the pcb's silkscreen.

As you solder the diodes in, with the leads passing through the board, note that in each cases one should make contact with the large area of unetched copper on the board's underside, but the other should NOT. The little gap between the plated through hole and the ground plane is pretty small, and requires careful work.

Check the device still works. The diodes are to protect against things that can happen. As you will have gathered, they are not essential to the circuit's operation in simple circumstances.

Install the BAT54s: D9-D15. They go on the back side of the board, each occupying one of the trio of small square pads in the same line as D16-D22. Be careful you don't accidentally install any upside down.

Clean the board, to remove any flux that remains. Be sure the components have cooled. Use isopropyl alcohol. If you buy some rubbing alcohol for this job, be sure it isn't "enhanced" with oils, etc, which might be fine for your skin but won't help you with the next bits of soldering.

Once you have decided on how you will case up the pcb, you will know how long to leave the LED leads so that they fit nearly with the case. It is no accident that one lead of each LED is slightly longer than the other. I can never remember which is which, but once you discover which to attach to the positive pad of the diode's location on the pcb, that will be the right side for all of the other diodes.

.......... ENJOY!

(Now all we have to do is write the software.....)
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