Welcome
to part 4 of my Allstar Link node build.
In
this installment I will prepare some additional components in preparation for casing the project up.
Before I get started
In the last installment I covered modifying the popular CM108 USB sound module for use with the Allstar Link Node and I remembered that I had used the CM108 in a digital modes interface that I designed and built back in 2018. Below is a photo of the interface completed.
Click for a larger image
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| Click for a larger image |
From the images above you can see that I modded the CM108 so that it would plug into a set of headers on my interface board, I did this as it was cheaper to buy the CM108 USB stick than it was to purchase the actual chip!
I have never been happy with my approach of bodging the CM108 to my interface board, it is not very professional and it feels half baked so
I have decided that I am going to redesign the PCB so that the CM108
chip and its accompanying components are where they should be on the
main PCB. I will document this in a future blog post in the near
future and post the schematic etc.
In the mean time I decided it would be fun to draw out the schematic of the CM108 USB sound module for future reference so here it is.
**** Schematic updated on 27th February 2021****
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| Click for full size schematic |
Getting back to business
I decided that I wanted to enclose my node in a metal enclosure so that it was shielded and not another source of unwanted interference in the shack, the node is in its own right a mini computer and there is a reason why computers are built into metal boxes!
When thinking about boxing the node up I decided that on the front panel I would have an on/off power switch, a node halt push button, a power on LED and a node status LED.
On the rear panel I will mount a CAT5 network socket and a power supply socket.
As I am building my node into a metal enclosure the onboard WIFI of the Raspberry-PI computer will be shielded and unusable, that is why I have opted for a hard wired CAT5 connection to the node.
Whilst WIFI maybe more convenient it is not as fast or reliable as a hard wired connection. Most households have multiple devices connected via WIFI such as laptops, tablets, mobile phones, smart televisions & other cloud based services all of which weigh down a wireless network and introduce lag. Hard wired on the other hand allows for faster and more reliable data transfers with each device being fed from its own dedicated connection back to a router and high speed network switch.
Preparing the LED's
For the front panel I am using a 5mm Red LED for the power indicator and a 5mm RGB common cathode LED for the node status using just the blue and green chips/pins.
Both LED's are mounted on small pieces of FR4 stripboard cut to 4 holes by 4 holes for the RGB LED and 4 holes by 2 holes for the Red LED. I cut breaks in the copper strips with a small drill bit where the surface mount resistors will be placed, the following image show the PCB's prepared ready for mounting the components.
I used 1206 size SMD resistors and mounted these on the PCB's along with the LED's note the resistor values and LED orientation In the next image.
I stripped individual cables from the ribbon to colour match the LED's, this makes it easy to identify the cables when connecting them to the Raspberry PI board later. For the RGB LED I cut the cables to a length of 80mm and for the Red LED 60mm, this is ideal for the enclosure I have chosen and the component layout. The image below shows my completed LED's with panel holders.
The LED resistor values
The Raspberry PI GPIO header is assumed able to provide 16mA maximum current per GPIO pin or a combined current of 50mA when using multiple GPIO pins. I have not been able to find concrete information to confirm these ratings but in general the IO pins would be buffered so I will accept my findings to avoid the risk of damaging the PI board.
For the node build I will be using 2 of the GPIO pins to drive the RGB status LED, the Red power LED will be fed from the main 5 volt power supply and not from a GPIO pin.
Based on standard diffused LED's the maximum forward current drawn from the RGB LED would be 40mA (20mA per colour) which exceeds the suggested GPIO limit of 16mA per pin.
To limit the current drawn from the GPIO pins a series resistor is placed in the LED anode path which will also act as a control over the LED brightness, this is great as the RGB LED is uncomfortably bright when driven at full whack.
After a bit of experimenting I settled on 220 ohm for the Red LED and 1000 ohm for the RGB LED, these values provide clear and adequate brightness and the maximum current drawn per GPIO pin is a mere 2.5mA.
Node halt switch
As mentioned previously the Allstar Link Node is a mini computer in its own right, it is built around the small form factor Raspberry PI and like any other computer it must be shutdown in a controlled manner, failure to do this may result in corruption of the operating system and failure of the node.
I will be using the Hamvoip software for my node and thankfully the software includes a script to do the controlled shutdown. For my build I am going to include a push to make switch to do the job but I believe it can also be done remotely with DTMF code.
I wired my push switch with two more of the Dupont ribbon cables cut down to a length of 100mm. Here is my completed node halt button.
Node power switch
For the main on/off power switch I am using a miniature SPDT (single pole double throw) toggle switch rated at 3 Amps.
To prepare the switch I attached two wires, one 180mm in length and the other 110mm, I used different coloured cables salvaged from computer power supplies, they are 2mm in diameter and a little overkill but what will do a lot will do a little!
Here's the switch prepared ready for casing the project up.
DC power socket
My node will be powered from a 5 volt DC Raspberry PI plug in mains adapter, this will then connect to the node via a DC power connector mounted on the rear enclosure panel.
I used a 2.1mm DC power connector sourced from ebay, I soldered a 100mm length of black insulated wire to the outer case terminal and 150mm of yellow insulated wire to the center pin terminal as illustrated below.
Well that is it for this installment, all of the parts that need preparing for the enclosure are done.