Hello, I bought a six pack of IV 9 numitrons, and I am wondering how to run them, preferebly from an Arduino Nano.
IV 9 is running at 4,5 v, and needs 19,5 mA per segment, and it has 8 segments, meaning
0,7 W per bulb.
I thought perhaps to buy a 4,5 v power supply, and use transistors to control it from the Arduino, but I'm unsure how to get the correct current to each segment.
My questions: Can I run it directly from an Arduino?
To reduce voltage from 5 v to 4,5 I need to resistors, and 1 to reduce current, meaning 3 resistors per segment. Isn't there a simpler way?
I do have some experience with Arduino, but as you see I'm not so good with electronics, so help is appreciated
19.5 mA can be driven from an Arduino pin; but it's really at the limit for the pin. Eight of them means 160 mA, which is close to the 200 mA overall limit for a single ATmega328p chip. So yes, possible, but doesn't sound like a good idea for a long term project.
Then I may assume you will want to use all six of them at the same time. That's going well over the limit for an Arduino. You need an external driver, most convenient will be something like the TPIC6B595 high power shift register - one for each Numitron tube. Remember to add a 100 nF capacitor at each shift register's power pins.
I saw these things are rated 3.5-4.5V, so the 4.5V is the limit. A few solutions for this.
power your whole project at 3.5-4.5V. The Arduino will be perfectly happy, especially if you reduce the clock speed to 8 MHz (you may use the internal oscillator - rely on your RTC for accurate time, not on the internal timekeeping). Or just get a 3.3V 8 MHz Pro Mini. Minimum to run on 16 MHz is about 4.2V, so that's still in range.
power the whole project at 5V and place one or two diodes in series with each Numitron segment. Each diode gives about 0.5-0.7V drop. So one gives a pretty bright display (you're at or near the upper limit); two of them get you in the middle of the operating range.
power your Arduino from a 5V source, the Numitron from a separate 3.5-4.5V source. Do remember to share grounds.
The easiest way to get 4V is an adjustable buck converter. 12V in, 4V out. You may not get away with dropping 5V to 4V, this dropout may be too low for the buck converter. Most have a minimum drop.
I'd go for option 1 using a 3.3V 8 MHz Pro Mini board. That sounds to me the most straightforward.
Option 2 is a good second, especially if you have a bag of spare diodes (8x6 segments means 48 or 96 diodes) and enjoy soldering.
Is this for a clock? Then a WeMos D1 mini (internet timekeeping) and six TPIC6B595 chips could work.
Can all be powered with a single 5volt cellphone/tablet charger, with the diodes that wvmarle mentioned.
An experienced tech would use this 3.3volt buck converter to power the numitrons (no diodes).
And increase to the desired voltage by switching resistors (or LDR+resistor) parallel to R2.
Leo..
I have some TPIC6B595N shift registers, and also a shitload of diodes, so I think I will go for that solution.
I don't think I fully understood how shift registers are going to help me though. I know they can expand my pins, but the Arduino can still not supply enough current?
To me it seems nice to use an external power to the numitrons, and use diodes to get the right voltage. It would be nice to power aruino and the Numitrons from the same 5 v supply. How am I shure I get the right current thought?
I think I'm going to try to get one Numitron working before I use all 6. Thank you for the help
Einar_Nordvik:
I don't think I fully understood how shift registers are going to help me though. I know they can expand my pins, but the Arduino can still not supply enough current?
The TPIC shift registers are just eight switches with a common ground.
All the display current is flowing through those switches, and none through the Arduino itself.
Do you have a link to the product page or datasheet of those numitrons?
Leo..
The TPIC version of the shift register is basically a regular shift register + transistor in the output.
Make sure you power the shift registers directly from the power supply (which of course can power the Arduino as well), and that you have at least 1A of current available.
Connect the common (pin#1) of this numitron to 4.5volt (5volt with a 1N4004 diode in series).
And the seven segments and DP to the eight outputs of a TPIC6B595.
Look for examples to drive a more common 74HC595 with a 7-segment display.
Driving the TPIC is the same.
Leo..
P.S.
The enable pins can be connected to a PWM pin, for brightness control.
