Alioth's Journal: [Z80] Pressure sensors, and further meddling

Well, the good people on NEONIXIE-L knew of the pressure sensors I was looking for, so now I've found a choice from the cheap (about $20) to the not so cheap ($200). The latter sensor is very clearly for measuring atmospheric pressure. The cheap ones do from about 150mb to about 1100mb, so the resolution in the area of interest (approximately 900 to 1050mb) is pretty poor, but reading the datasheets for them, it looks like the minimum voltage step is good enough for 1mb resolution (although for the ADC to have sufficient resolution, the analogue ground will need to be +3v or so with respect to digital ground, I'll have to test the ADC to check it doesn't start doing strange things).

I also added a latch + blinkenlights to the breadboard tonight to check that the latch I intend to use for sideways ROM/RAM select works at full speed (which it does, the data sheet said it would so it's not surprising that it does. But it's kind of a 'worst case test' since the stray capacitance must be really building up on the breadboarded data bus now, given the length of the data bus).

So there's really nothing for it; aside from obtaining a Z80 CTC for some timing functions, I need to lay out the "core board" for the system. The core board (I suppose you could call it a motherboard) will contain the things I would like on pretty much any 8-bit CPU project: ROM, RAM, PIO and CTC and sideways memory paging logic. I hope to squeeze this all on a single 6 x 4 inch double sided PCB. This should be doable now I can confidently do it as a proper 2 layer board (earlier efforts were to keep virtually everything on one side so as to use single sided board and some interconnects here and there). I'll probably use IDC cabling for the bus connection between boards.

Pressure sensor prices

[SynapticNoise]

$200 for an accurate pressure sensor sounds about right. A few years back, we were looking for a weather probe for the observatory. We found a compact outdoor unit that measured temperature, rel. humidity and atmospheric pressure. They claimed the unit had 1/50 mb accuracy and it reported in 1/100 mb precision. The unit was self-contained and needed only a 4-conductor cable (+V, RD, SD, Gnd). It communicated via a long-haul serial and had a small adapter box at the receiver side that converted the long

Re:

[Alioth]

Incidentally, this:

http://uk.farnell.com/jsp/endecaSearch/partDetail. jsp?SKU=540894 [farnell.com]

is the 'expensive' one at Farnell. The NovaLynx one I looked at did the same thing at the same range but was almost three times as expensive (presumably if I look carefully at the datasheets for both, I'd probably find the expensive one has better resolution, but given it will feed into an 8 bit ADC the resolution doesn't actually have to be that great). Since these particular devices measure 800-1100 mb, I'll have to cut it