but sounds like it would be a race condition

No race condition, on clock all SRs shift in whatever is preseneted on their input pin and this has been stable since the last clock. So they all sample stable data at exactly the same time.

You didn't say what the "devices" were but as this is an EPROM emulator I assume 64k SRAMS?

In that case they have CS inputs so you can control them individaually,

set address with the SRs
select the active SRAM
read/write pin = 0
read/write
read/write pin = 1

Normally though with an emulator (unless you're using dual-port RAMs) you need to mux the data and address lines as well. Is that the case here?

Do you need to use counters? Is that because you want the speed of just pulsing once per read/write?

Do the devices have chip select pins? With 2 shift regs and one Arduino pin per device (if they have CS) you're done.

The pic was a jpeg but the link points to

http://c/Users/JD/Desktop/gauge%20panel.jpg

Probably not going to work  

Sorry 2stl, just realised that thread was yours so I guess you knew about it  

There was a thread about almost this exact problem (218 inputs) the other day.

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1281702590/0

multiple items will share (and spread out) the load.  Is that true for having multiple servos (so each is effectively getting 4.5v, not 9)?

If you had say two light bulbs they could be wired in series and therefore get 4.5v each. In this case however the servos are in parallel, therefore they both get 9v and that's too high.

Re the voltage tap idea, in general it's a bad idea to take a tap from a battery bank. As lefty says you will get different discharge rates for the batteries (it will work and maybe that doesn't matter if you pull the batteries and put them in a charger, but it's not best practice) . If you are tapping for a 10W light from a 400Ah bank then what the heck, but to pull large currents from the center of a bank is never good practice.

Spec says 4-6V.

They run warm; it may be a normal temperature.  Should 9V be okay?

Um, you do the maths.

but what's 4d

Print as 4 decimal digits.

% is not modulo in this case, it's a meta character that flags the following format string.

All the above ? about noise etc have to be addressed. Having done so, look at the two voltage levels you are receiving from your PIR at the Arduino end, then hook up a comparator with a compare voltage half way between the "high" and "low" values, this will clean up your signal and produce 0-5v levels for the Arduino.

My servos are recommended 4.8-6.0v

As are most I think.

Have you tied the GND of the battery pack and the Arduino together?

Also the TRACO TSR-1 series, up to 96% efficient, up to 36v input with no heatsink required.

Remember that a simple beam breaker can't deal with two people entering/leaving at the same time or someone half entering then changing their mind.

I had an arse-covering paragraph though.

May need a resistor from AIN1 to GND to get some current flowing through the diode.

Anyway I've got a better idea, use a MAX6818 debounce chip, this will debounce up to 8 switches and has a "input changed" output (CH).

Run CH to a pin to cause the interrupt. Run as many of the 6818 outputs as required (5 I guess) into an R2R network and from there into an ADC input.

You get an interrupt after the switch is debounced and read the voltage. Two pins and easy software, plus you get really good ESD protection and can have +-25v on the inputs.

[NOTE: I spent some time on this then realised it won't work because the quescient state is the same as the interrupt state ie AIN0 > AIN1 but it's late and I'm too tired to think about it any more so I'll post it anyway in the hope it might give you a start.]

Being a newbie, I

Sorry, I thought you meant to programming in general.

If you're happy to use the analogue comparator IPs...

NOTE: I spent some time on this then realised it won't work because the quescient state is the same as the interrupt state ie AIN0 > AIN1 but it's late and I'm too tired to think about it any more so I'll post it anyway in the hope it might give you a start.



In the quescient state ADCn and AIN0 at the same voltage level and AIN1 is 0.6v lower.

When a button is pressed ADCn goes immediately to Xv, AIN1 goes immediately to Xv - .6.

After a short time (and when the switch has stopped bouncing) AIN0 reaches Xv which is higher than the X - .6 on AIN1 which causes a comparator interrupt and the ISR reads ADCn etc etc.

May need a resistor from AIN1 to GND to get some current flowing through the diode.

No thought put into what happens when the button is released.