Mobile Basestation Construction : USDA ARS

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Mobile Basestation Construction

General Soldering Instructions
Set the temperature of the soldering iron between 700 to 750 degrees F. You may need to experiment and adjust your iron temperature to better suit your particular iron, tip, and solder. We have used fine-pointed tip with 0.56 mm dia. 60% tin/40% lead 5-core solder will good success at this temperature.

Prior to soldering, prepare the tip of your soldering iron. Cold shock the pre-heated tip on a damp sponge and wipe the tip clean. Finally, tin the tip with solder. Repeat this process when the tip becomes fouled with flux resin, carbon, and other debris.

When soldering, particular on small and/or heat-sensitive parts, do not apply heat too long in one area of the part. Many electronic parts are heat sensitive and can be ruined by holding the iron in one place to long. Allow heat to dissipate by soldering a contact at one end or side of the part then move to a contact on the opposite end or side of the part to continue soldering. Where all the contacts are close together on one end or side of the part, you may need to pause for a few moments in between soldering each contact to allow heat to dissipate.

Placing a small part in its proper place on the PCB and keeping it there during the soldering process can often be maddening. Low-tack tape or small, padded alligators clips can be helpful. Another useful approach is to load the iron tip with a slight excess of solder, then hold the part in place using tweezers or a dissecting needle held in your off hand, tack one contact of the part with the loaded tip, check the part for proper alignment and reheat and adjust, if necessary. Then, solder two different contacts (preferably on the opposite sides/ends of the part) in place with ample solder. Now you are free to properly solder the tacked contact and all other contacts on the part.

After soldering has been completed on a part, double-check all the contacts (with a magnifying glass, if necessary) to make certain that there are no solder joints bridging across contacts. If a bridging joint is found, you may be able to remove the bridge by stroking the iron tip between the affected contacts. If there is a slight excess of solder in the joint, this solder may be displaced by pushing it along one contact with the iron tip. If there is just too much solder in the joint, use a soldering wick (copper braid) to wick-up/remove some or all the solder. When finished soldering, clean and tin the iron tip to prevent corrosion and then turn off the iron.

Assembling the Mobile Basestation Electronics

Sequence of Components in the Assembly

1 Printed Ciruit Board (PCB), custom
2 resistors, 10 Ohm, surface-mount
1 socket, 20-contact, 2-mm pitch, dual-row, surface-mount
1 RS-232 transceiver/driver, through-hole mount
4 capacitors, 0.1 uF, through-hole mount
2 capacitors, 10 uF, surface-mount
1 regulator, 3.3 V output, surface-mount
1 power cable, 2-wire
1 communication cable, PWC-22, Gomadic, 8-wire
1 spread spectrum radio transceiver, through-hole mount
1 radio antenna, 900 MHz, flexible (rubber duck)
1 PDA enclosure,
1 Enclosure pod kit,
1 Personal Digital Assistant (PDA), w/ serial port

The bill of materials for the mobile basestation is available

Assembly Instructions

Wondering where to get the mobile basestation PCB? The Gerber files and an example quote to be used when ordering the PCBs are available on the Purchasing Materials page.
Use the white silk-screen legend on the PCB to identify where each electronic component should be mounted.
Many parts have polarity, so take note of polarity notations on the part and PCB.

Apply liquid flux to the 2 pads designated, on the top-side of the PCB, for one of the 2 resistors.
Place a resistor on the PCB, centered over the 2 pads, and hold in place with tweezers. There is no polarity in this part so, you do not have to be concerned with "which end goes where?". Tack one end (contact) of the resistor in place using a loaded iron tip. Check for proper positioning and adjust, if necessary.
Solder the opposite end of the resistor, applying most of the heat to the pad and using a length of solder (held in the off-hand) to supply ample solder to the joint. Repeat on the tack joint of the opposite end. This is a small part so, be careful not to allow the iron tip to linger on the part. Repeat this entire procedure for the second resistor.

Apply liquid flux to the 20 solder pads, on the top-side of the PCB, for the 20-contact socket.
Place a socket on the PCB, with the contacts centered over the pads, and hold in place with tweezers. There is part does not have polarity. Tack one contact on the end of the socket to a pad using an iron tip pre-loaded with solder. Check for proper positioning and, if necessary, re-heat the tack joint and adjust the socket position.
Tack a contact on the opposite end of the socket to the PCB. Confirm proper positioning of the part. Solder the remaining contacts to their respective pads, applying most of the heat to the pad and using a length of solder (held in the off-hand) to supply ample solder to the joint. Reheat each of the 2 tack joints and apply ample solder to finish these joints.

Place a right-angle bend in each contact, about 8 mm from the body of the capacitor, so that the contacts can be inserted into the 2 through-holes associated with each capacitor. If the bends are done correctly the body of the capacitor will be centered between the 2 through-holes and the part with fall out of the holes if the PCB is inverted.
With the PCB positioned bottom-side up, apply liquid flux to all 8 through-holes designated for the 4 capacitors. This part, like all capacitors, has polarity. Insert each prepared capacitor (contacts properly bent) being certain that the contact associated with the conical end (positive end) of the capacitor is placed through the hole designated with "+" in white silk screening.
Invert the PCB, while using one hand to hold the capacitors in place, and place the PCB top-side up on the bench. Confirm that the contacts of each capacitor are fully-inserted through the holes. Solder each of the contacts to their respective through-hole, applying most of the heat to the through-hole collar and using a length of solder (held in the off-hand) to supply ample solder to the joint. Solder in each joint should wick entirely through the hole and appear on both sides of the PCB as a slight cone surrounding the capacitor contact. Use small side-cutters to clip off the excess from each contact.

With the PCB positioned bottom-side up, apply liquid flux to the 20 through-holes designated on the PCB for the 20-pin RS-232 transceiver/driver.
This part does have polarity. The dimple on the top corner of the transceiver/driver designates pin number 1 on the part. Position the part so that pin #1 passes through hole #1 as designated with a silk-screened, white number "1" on bottom-side of the PCB. All pins of the part should pass through the PCB and protrude slightly and equally from the top-side of the through-holes. Invert the PCB, check positioning of the part, and tack one of the pins on the end of the part to the through-hole collar, on the top-side of the PCB, using an iron tip pre-loaded with solder. Confirm proper positioning and then tack one of the pins on the opposite end of the part to its through-hole.
Solder the remaining pins to their through-holes, applying most of the heat to the through-hole collar and using a length of solder (held in the off-hand) to supply ample solder to the joint. Solder in each joint should wick entirely through the hole and appear on both sides of the PCB as a slight cone surrounding the pin. Apply ample solder to the 2 tacked pins to finish these 2 joints.

Apply liquid flux to the 2 pads designated, on the bottom-side of the PCB, for one of the two capacitors (10 uF).
Place the capacitor on the PCB so that the marked end (white stripe) of the capacitor is positioned over the pad marked "+" in white silk screen.
Hold the capacitor in place with tweezers. Check that the capacitor is centered between the 2 pads. Use a loaded iron tip to tack one end (contact) of the capacitor to a pad. Check for alignment and adjust if necessary by nudging the part or re-heating and re-positioning the part.
Solder the opposite end of the capacitor, applying most of the heat to the pad and using a length of solder (held in the off-hand) to supply ample solder to the joint. Repeat on the tack joint of the opposite end. Repeat the entire process for the remaining capacitor.

Apply liquid flux to the 5 small pads and 1 large pad designated, on the bottom-side of the PCB, for the regulator.
Place the regulator on the PCB, aligned over all the pads, and hold in place with tweezers or a finger tip of the off-hand. The large pad is a bit small for the part, so slightly slide the part towards the 5 smaller pads until the edge of the large pad can be seen above the top edge of the heat-sink portion of the part. Be certain you can still see some of each of the 5 pads extending beyond the 5 regulator contacts.
Using a loaded iron tip tack one of the 5 contacts to its pad. Check for proper alignment and adjust, if necessary. This part is difficult to de-solder so, make certain you have it position where you want it before proceeding.
Solder each of the remaining contacts on the regulator, applying equal heat to both the pad and contact, and using a length of solder (held in the off-hand) to supply ample solder to the joint. Be careful not to apply too much solder as the 5 contacts on this part are prone to forming bridged solder joints.
Drag a clean, unload iron across the 5 solder joints to smooth and evenly distribute the solder.
Inspect the joints with a magnifying glass and repair any bridging joints.
Using a loaded iron tip, apply heat to an upper corner of the heat-sink portion of the part and to the pad. Slow drag the iron tip back and forth across the whole upper edge of the part, thus heating the entire heat sink, until you see the solder from your iron begin to wick under and along the heat sink. Using a length of solder (held in the off-hand), form a solder joint completely across the upper edge of the heat sink portion of the part. This last solder joint allows heat transfer from the regulator to a larger heat sink (i.e., the copper layers of PCB itself).

Cut 12-inch (30-cm) lengths of 22 or 24 gauge wire, one length with black insulation and one with red insulation. We use lead wires (wire used to make leads for multi-meters, etc.) because of their flexibility.
Strip about a 1/8 inch (3 mm) of insulation off each end of the wires.
With the PCB oriented top-side up, locate the 2 plated holes on the PCB designated for the main power cable (VIN). Insert the bare end of the red wire through the hole marked with "Vin > 3.6V".
Withdraw the wire from the hole slightly so that some of the bare end is visible between the insulation and the top rim of the hole. Apply liquid flux on the bare wire and down the hole. Using a loaded iron tip, tack the wire in place.
Reload the iron tip and touch the tack joint thus adding more solder to the joint. While the solder in the joint is still molten, push the wire back down into the hole so that the insulation is in contact with the top rim of the hole.
Repeat this soldering process with the black wire inserted in the adjacent hole marked with "GND". Invert the PCB and inspect the 2 plated holes with a portion of the ends of the power cable wires now extending out of them. During the soldering process, solder should have wicked down the holes and pooled around these wire ends. If no solder is visible, carefully hold the affected wire in place (i.e., so the wire does not back out of the hole when the solder is reheated) and apply some solder to the bottom of the hole and the wire ends. When finished the solder should form a nice cone around the wire end. If necessary, repeat for the other wire. Use small side-cutters to cut of any excess bare wire end protruding above the solder joint.

Cut the cable to about 12 inches (30 cm) in length and carefully strip off the outer insulation and aluminum shielding material from the cable. Slip a 1-inch (25-mm) length of 1/4-inch (6-mm) dia. heat shrink tubing over all wires in the cable, except the orange, yellow, and white wires, then slide the tubing down towards the cable connector where it will not fall off the cable. Slip a 1/4-inch (6-mm) length of 1/8-inch (3-mm) dia. heat shrink tubing over each of the green, blue, gray, and brown wires of the communication cable.
Using a sharp razor blade or fine-wire stripping tool, strip about 1/4 inch (6 mm) of insulation from the green wire, which is associated with the RTS contact on the cable connector. Insert the bare end of the green wire through the hole labeled "ACRTS" in white silk screen. Invert the PCB and solder the wire to the through-hole collar while using a solder iron set to low heat (500-550 degrees F) and applying all the heat to the collar of the through-hole. Be quick and be careful as the insulation of this fine wire melts easily if the wire is heated excessively.
Strip and solder the blue wire to the through-hole labeled "ACCTS" in white silk screen. Repeat for the gray wire and hole labeled "ACRXD" and for the brown wire and hole labeled "ACTXD".
Cut a 12-inch (30-cm) length of fine (28 gauge), black wire from a stock spool and strip 1/4 inch (6 mm) of insulation from one end. Strip the end of the black wire found in the communication cable and twist the bare ends of the 2 wires together. Slip a ?-inch (6-mm) length of 1/8-inch (3-mm) dia. heat shrink tubing over both black wires and slide it down out of the way. Insert the twisted ends through the hole labeled "GND" which is adjacent to the hole labeled "ACTXD". If you have difficulty inserting the twisted ends, you may need to use a length of finer wire.
Slip the heat shrink tubing for each of these 5 wires (green, blue, gray, brown, and black/black) up against the PCB and bend the 5 wires over so they are in contact with the top-side of the PCB, running left to right along the near edge (towards the power cable), and parallel with the top surface of the PCB. Use a heat gun to shrink the tubing while holding the wiring in place with a free hand.
Slip the ends of the power cable into the larger, 1-inch (25 mm) long heat shrink tubing that had previously been installed on the communication cable. Slide the tubing up the communication/power cable bundle until the upper end of the tubing is positioned as close as possible to the top-side of the PCB. The orange, yellow, and white wires of the communication cable should still remain on the outside of this heat shrink tubing. Use a heat gun to shrink the tubing while holding the wiring bundle parallel and in contact with the top surface of the PCB.
Slip a 1/4-inch (6-mm) length of 1/8-inch (3-mm) dia. heat shrink tubing over the end of the yellow wire so that the end of the wire is completely cover by the tubing. Use a heat gun to shrink the tubing. Repeat for the white wire. These 2 wires are currently not required and purpose of this heat shrink covering is to help prevent shorting of these wires. The last wire (orange) will be connected to the power supply jack for the PDA (see below).

Assembling the Enclosure

Installing the Power Jacks and Switch
The instructions below describe how to install the 2 different jack connectors and a sealed rocker switch in the Through-Box-Pod kit for the hand-held (PDA) enclosure. The jack connectors supply power to the spread spectrum radio and to the Personal Digital Assistant (PDA). The rocker switch controls power to the radio.

Starting with the Otterbox Through-Box-Pod kit, use the allen wrench included in the kit to remove the face plate from the pod. Use an 11/16-in (17-mm) drill bit or panel-cutter (round) to create a hole for the radio power rocker switch in one of the long sides of the box portion of the pod kit. The center of this 11/16-in (17-mm) hole should be located 1 inch (25 mm) from one of the short sides of the box and centered within the width of the box.
Mount the box portion of the Through-Box-Pod kit to the Otterbox 3600 PDA enclosure using the instructions included with the kit. Route the radio ground wire (black, 22-24 gauge), which comes from the basestation PCB (see above), through the box portion of the pod kit from inside to outside of the PDA enclosure. Do the same with the orange and black (PDA ground) wire associated with the communication cable. Slip the plastic mounting nut of the rocker switch over the end of the radio power wire (red, 22-24 gauge), which also comes from the PCB, and slide the nut up the wire (towards the PCB) and out of the way. As done with the black, radio-ground wire, route this red, radio-power wire through the box portion of the pod kit but exit out the 11/16-in (17-mm) rocker switch hole rather out the end of the box.
Drill a 5/16-in (8-mm) hole about ? inches (19 mm) from one of the short sides of the face plate. The hole should be centered within the width of the face plate.
Drill a ? -in (6-mm) hole in the very center of the face plate. This ?-in (6-mm) hole will be used by the PDA power jack to be installed later (see below). Position the face place with the outside facing up and use a 3/8-in (10-mm) drill bit to counter sink the ?-in (6-mm) hole slightly. The barrel of the PDA power jack is a bit too short to successfully be installed through the face plate without the counter sinking. We have not been able to find a suitable replacement for this part.
With the inside surface of the pod face plate facing up, apply a small amount of silicon sealant around the hole. Insert the threaded barrel of the radio power jack through the hole. Invert the face plate and install the flat washer and nut on the power jack and tighten the nut to seal and secure the power jack in place.
Find the loose end of the black (ground) wire of the power cable constructed above. Slip a 1/4-inch (6-mm) length of 1/8-inch (3-mm) dia. heat shrink tubing over the end of this black wire and slide the tubing down the wire and out of the way. Insert the bare end of the black wire through the hole in the end of the ground tab on the radio power jack. Solder the black wire to the ground tab of the power jack, while applying heat primarily to the ground tab.
Cut a 6-inch (15-cm) length of red wire (22-24 gauge) and strip about 1/8 inch (3 mm) of insulation from both ends. Slip a 1/4-inch (6-mm) length of 1/8-inch (3-mm) dia. heat shrink tubing over the end of this red wire and slide the tubing down the wire and out of the way. Insert one bare end of the red wire into the hole on the power tab of the radio power jack. Solder the red wire to the power tab, while applying heat primarily to the power tab.
Slide the heat shrink tubing (2 pieces) up over the solder joints so that the bare wire ends and tabs on the radio power jack are covered. Use a heat gun to shrink the tubing.

With the outside surface of the face plate for the Through-Box-Pod kit facing up, apply a small amount of silicon sealant to the outside of the 1/4-in (6-mm) hole in the face plate (see drilling instructions in previous section). Insert the PDA power jack through the hole and tighten the nut against the inside surface of the face plate (Note: this installation procedure is just the opposite of that for the radio power jack).
Cut the orange wire, which was contained in the communication cable (see above), to about 8 inches (20 mm) in length. Strip 1/4 inch (6 mm) of insulation from the end of the orange wire. Slip a 1/4-inch (6-mm) length of 1/8-inch (3-mm) dia. heat shrink tubing over the end of the orange wire and slide the tubing down and out of the way. Insert one bare end of the orange wire into the hole on the power tab of the PDA power jack. Solder the orange wire to the power tab, while applying heat primarily to the power tab.
Strip 1/4 inch (6 mm) of insulation from the end of the black wire (black wire which was twisted together with the black wire of the communication cable - see above). Slip a 1/4-inch (6-mm) length of 1/8-inch (3-mm) dia. heat shrink tubing over the end of the black wire and slide the tubing down and out of the way. Insert one bare end of the black wire into the hole on the ground tab of the PDA power jack. Solder the black wire to the ground tab, while applying heat primarily to the ground tab.
Slide the heat shrink tubing (2 pieces) up over the solder joints so that the bare wire ends and tabs on the PDA power jack are covered. Use a heat gun to shrink the tubing.

Installing the Grounding Plate, PCB, and Radio Transceiver
The instructions below describe how to install the aluminum grounding plate, the basestation PCB and associated mounting hardware, and the spread spectrum radio transceiver inside the hand-held (PDA) enclosure. The grounding plate increases the ground plane used by the radio transceiver and provides a solid base on which to mount the basestation PCB. The spread spectrum radio transceiver plugs into the 20-contact socket on the PCB and is held in place with the PCB mounting bolts.

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U.S. DEPARTMENT OF AGRICULTURE

Northwest Watershed Research Center: Boise, ID

Sequence of Components in the Assembly