Re: [smartsockets] IV-17 / IV-4 Smartsockets
- --- In firstname.lastname@example.org, John Rehwinkel <jrehwin@...> wrote:
>Sorry John, but the accuracy is important because the crystal is also
> > To improve on that, I clocked the pic from an external 24MHz crystal,
> > to get the SPI bus up to 6MHz, and now the fading is very smooth. The
> > problem here is that the cost of the crystal could be more than you
> > might pay just for one tube !
> Surplus is your friend. Electronics Goldmine has 24MHz crystals for a
> dollar apiece. As they're surplus, they may not be the most accurate
> crystals out there, but accuracy doesn't matter here. Goldmine
> usually deals in quantity, so I suspect they have a large number
> available, and may even give a discount on a quantity purchase.
the timebase for the USART serial port, although I am not sure to what
extent a few ppm of crystal error at 24MHz changes the port speed.
I had some issues with internal oscillators running at 4MHz being
- --- In email@example.com, guus.assmann@... wrote:
> Wasting power is not good, as a general rule.
> But in a case like this, it's such a small amount.
> And one could also say that powering up any smartsocket is a waste
>Yeah, but hopefully they won't ever say that !
I've just done some real measurements and had a pleasant surprise.
At 24V the long diagonal segment (chosen because it was the longest)
runs at about 140uA (microamps). As voltage rises so too will current,
but it's probably enough for now to say that each segment draws 200uA,
to be on the safe side.
If , on average, only half of the segments are used, the average
maximum current lost in the driver will be no more than about 2mA.
Compared to a 'proper' VFD high side driver like the MAX6921, which
draws about 1mA in idle mode, and has serial bus lines and blanking
control lines which could easily add 10mA, using resistors and drivers
seems to be less wasteful than a proper VFD driver is !(under certain
circumstances ;o) )
Now, looking again at the choice of driver IC's can anyone see
anything wrong with using three ULN2003AD chips at 15 pennies each ?
(less in larger quantities). They are rated to 50V with a relatively
huge current capacity. I have some on the shelf so I think I'll give
them a try in the next couple days.
The other thing missing from the equation are the resistor networks
which would be required to add current limiting to each segment which
is to be shorted to ground, just pennies in terms of cost, but need to
find room for them on the pcb too !
- --- In firstname.lastname@example.org, Quixotic Nixotic <nixotic1@...>
>Apparently they live longer, and also draw slightly less current too.
> Does anyone know why the IV-17s are better than the IV-4s? What is
> the difference, electronically-speaking?
> John S