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Cabinets

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Here are some ideas for cabinets. There are a few things that are must-haves.


Radios:


Types of TNCs

At this time there are two known good solutions and a maybe-coming-soon solution. In our network, the TNCs may be mixed and matched. In your cabinet, you may make choices.

TNC‑PI

Coastal Chipworks and G8BPQ have created a TNC which attaches to the I2C bus on the Raspberry PI, permitting a large number of TNCs to be attached using just a ribbon cable. This is elegant and cheap. The TNC‑PI was designed to be stacked on top of a Raspberry PI using a 40-pin (or 26-pin) connector which is female on the bottom and male on the top. This connector conceivably allows several TNCs to be stacked. Doing so, however, blocks access to the important transmit level control and makes it difficult to see the PTT and DCD lights. Instead we can use the ribbon cable to string the TNCs together eliminating this problem. 2014_n40901_cropped_rotatedx300
For more information on the TNC‑PI, see the TNC‑PI General Info page.
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When building for the TNC‑PI, you'll want to position the TNCs so they can be ribboned together, where the TNC LEDs are visible, and where the TXLEVEL screwdriver adjustable potentiometer is accessible.

The TNC‑PI is powered via the ribbon cable. The ribbon cable can be several feet long and the Raspberry PI does not need to be at the end, or any particular end of the ribbon.

The 40 or 26 pin header should not be installed. Instead a trivial 2 x 5 pin header is placed on the top of the board and soldered from the bottom.
Below left, Raspberry PI with header modified for 2x5 ribbon cable connector. Pins 11 and 12, GPIOS, are removed to permit the IDC connector to fit. Pin 7, GPIO, is also removed so audio on the ribbon cable on that connector is left unmolested by the Raspberry PI.
See 6 photos below showing TNC‑PI outfitted with 2x5 below.

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TNC Emulation using embedded computer

There are a couple of different software packages available for embedded computers to emulate the function of a TNC. There are two ways this can go for us. One is that we could create a stand-alone TNC-replacement which plugs into the TARPN Raspberry PI via USB. The other is to add the TNC functionality into the TARPN Raspberry PI. The first is more scalable but that may be a temporary limitation.

If we do use an emulated TNC, we will probably need a new interface card for the radio, even though that card won't be a real TNC. Stay tuned.


Example cabinets

Skip's first node cabinet design uses a lexan glued interior on the right to present the TNCs out front. The Raspberry PI is mounted with its LEDs facing front just above the TNCs. A commercial surplus switching power supply and gel-cel battery are contained within the lexan enclosure. Removable shelves hold the radios. The association between the TNCs and radios is obvious.
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This was an early node cabinet used at the JENRET:KM4IFV node site managed by KA2DEW. The radios are tie-wrapped into chicken-wire shelves. This provides great ventilation. Note the stacked TNCs and Raspberry PI. 201411_jenret_i6_03171sm

Fin's first node cabinet design aligns the TNCs and Raspberry PI on a removable wooden card which can be remove for service. In this particular cabinet a plastic shield may be placed over the front and a fan plus filter keep the wood-shop's dust from getting into the gear.
Fin said he plans to make cabinets like these for our local network builders who need them and can use them. Without the fan these cabinets are pretty easy for Fin to build.
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This 2 port node powers its digital section with an off-board 12v battery with charger and 12v to USB cigarette lighter adapter. The TNCs and Raspberry PI are tied down with tie-wraps. Radios are screwed down and power supply is velcroed and then strapped with tie-wraps. The extra DC wire is there to enable moving the power supply elsewhere. The board is 8" deep by 24" wide. The node had to fit on a shelf with only 8" of clearance. The entire package is removable as a unit for servicing.
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NC4FG built these 3 cabinets to use for a software development effort and for portable demo systems.
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The three cabinets below were one-offs with chicken wire under the radios.
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The following four photos show a cabinet made by Charlie, WA3UTC for his DAVIS node. It supports 4 radios. This cabinet was the genesis of the TARPN version of the TNC-PI providing a PTT test button and switchable audio feed to monitoring accessories.

In Charlie's node the TNC-PIs are connected via ribbon cables and the LEDs are brought out to the front panel. The audio from all 4 boards is mixed and presented to a high-impedance audio amplifier (so switching to monitor doesn't impact the received data signal) and also to a LED VU meter. This is fabulous for checking the quality and audio level on the link receive.

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