This is my first post and I am quite new to electronics. I have a couple of projects that I am working on, but this one could use a second (or many) set of eyes. I put the actual questions in bold, don't know if that helps.
Premise: Create a circuit for the display of numeric data ranging from 1 to 9,999,999 sourced from a REST web service.
Details. For clarity I will say that my company processes x amount of widgets per day. I would like to use nixie tubes to display a running tally of the day's work. The web-service is firmly in my wheelhouse so that part along with the appropriate data caching is not an issue.
What is an issue is the PCB layout. I have not yet decided which microcontoller I plan on using. My options are propeller, arduino, and raspberry pi. I think I can rule out the prop just based on ease of use. The arduino is easy to use, but wireless connectivity will have to be added in. The pi seems like the easy choice, but I am open to other suggestions.
Power: I have a separate power supply for the tubes providing 170V from 9V input. I will also need 5V for the drivers and shift registers which I plan to pull off the microcontroller. Since the drivers will be using the 5V and Gnd from the controller, but also need the Gnd from the 170V I will just tie the two grounds together. Do I need to do anything extra here for safety? I realize that we are talking about a ground, but I still want to make sure.
As far as the rest goes I plan on using (10) IN-12B nixie tubes (socketed) with (10) K155D1 drivers. Then use (5) 74HC595 shift registers daisy chained together for the numeric control. I am going to cheat and pretend that the decimal point indicator (DP elsewhere) is a comma and use it on the 1st,5th and 8th digit as a thousands separator. For this I plan on using an MPSA42 transistor. If my understanding of transistors is correct (which is shaky at best); I connect the collector of the transistor to ground and the emmiter to the DP pin (cathode; anode is always connected). Then if I supply +5V to the base the DP will turn on. What I absolutely guessed at is which transistor to use. I looked at a bunch of schematics for other projects and found the MPSA42 a common choice. Is the MPSA42 a suitable transistor and do I have the collector and emitters in the proper direction.
I used 22K resistors before each of the IN-12 anodes as those were the most commonly used, however, I am not so sure that is right for this case. Looking at the datasheet and spending a whole lot of time translating I find the following:
current display
digits = <2 mA
point = <0.3 mA
Current Operating with power from a DC voltage source
digits = 2 - 3.5 mA
point = 0.3-0.7 mA
Current Operating with power from the source of ripple voltage (average value)
digits 1 = 2 mA
point = 0.15-0.2 mA
Does this mean that 2-3.5 mA when the digit is turned on and then <2 mA to keep it lit?
If so wouldn't that be a 56K resistor? Or, keep a 22K for ripple (which apparently can be 50%)? [~7.7 mA]
Finally, how do I protect the DP since it cannot handle that amount of current (and it uses the same anode)?
I have attached a PDF file exported from DipTrace. I was going to post the actual DipTrace schematic but it looks like that is not allowed.
Sorry for the long read, I wanted to try and give as much information as I could. I have probably still left out details, please let me know if I did so. Any thoughts on the design would be appreciated.
Many thanks in advance.
Matthew
Premise: Create a circuit for the display of numeric data ranging from 1 to 9,999,999 sourced from a REST web service.
Details. For clarity I will say that my company processes x amount of widgets per day. I would like to use nixie tubes to display a running tally of the day's work. The web-service is firmly in my wheelhouse so that part along with the appropriate data caching is not an issue.
What is an issue is the PCB layout. I have not yet decided which microcontoller I plan on using. My options are propeller, arduino, and raspberry pi. I think I can rule out the prop just based on ease of use. The arduino is easy to use, but wireless connectivity will have to be added in. The pi seems like the easy choice, but I am open to other suggestions.
Power: I have a separate power supply for the tubes providing 170V from 9V input. I will also need 5V for the drivers and shift registers which I plan to pull off the microcontroller. Since the drivers will be using the 5V and Gnd from the controller, but also need the Gnd from the 170V I will just tie the two grounds together. Do I need to do anything extra here for safety? I realize that we are talking about a ground, but I still want to make sure.
As far as the rest goes I plan on using (10) IN-12B nixie tubes (socketed) with (10) K155D1 drivers. Then use (5) 74HC595 shift registers daisy chained together for the numeric control. I am going to cheat and pretend that the decimal point indicator (DP elsewhere) is a comma and use it on the 1st,5th and 8th digit as a thousands separator. For this I plan on using an MPSA42 transistor. If my understanding of transistors is correct (which is shaky at best); I connect the collector of the transistor to ground and the emmiter to the DP pin (cathode; anode is always connected). Then if I supply +5V to the base the DP will turn on. What I absolutely guessed at is which transistor to use. I looked at a bunch of schematics for other projects and found the MPSA42 a common choice. Is the MPSA42 a suitable transistor and do I have the collector and emitters in the proper direction.
I used 22K resistors before each of the IN-12 anodes as those were the most commonly used, however, I am not so sure that is right for this case. Looking at the datasheet and spending a whole lot of time translating I find the following:
current display
digits = <2 mA
point = <0.3 mA
Current Operating with power from a DC voltage source
digits = 2 - 3.5 mA
point = 0.3-0.7 mA
Current Operating with power from the source of ripple voltage (average value)
digits 1 = 2 mA
point = 0.15-0.2 mA
Does this mean that 2-3.5 mA when the digit is turned on and then <2 mA to keep it lit?
If so wouldn't that be a 56K resistor? Or, keep a 22K for ripple (which apparently can be 50%)? [~7.7 mA]
Finally, how do I protect the DP since it cannot handle that amount of current (and it uses the same anode)?
I have attached a PDF file exported from DipTrace. I was going to post the actual DipTrace schematic but it looks like that is not allowed.
Sorry for the long read, I wanted to try and give as much information as I could. I have probably still left out details, please let me know if I did so. Any thoughts on the design would be appreciated.
Many thanks in advance.
Matthew
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