PIC Selection + Application question

[Shinnster]

Hi all.

Which PIC would you recommend for the following requirements?

60+ solenoids used (their power will be isolated from the uC board) as output
60+ (BJT/FET)

They will be required to respond at the fastest rate possible and require more than 2 solenoids to be turned on simultaneously.

Any suggestion gurus? :thinker:

 

[Tunelabguy]

I doubt if you really need solenoids to be controlled in less that 1 usec. I would consider a cascade of shift registers driven by a data line, a clock line, and a parallel load line. What is your real timing requirement?

 

[Shinnster]

Haha not in microseconds yes. 100milliseconds. Shift register sounds good

 

[darkgnat]

do you need 60 solenoids turned on with BJT's? and if you use a shift register you better do some calculations, especially if it is 120, and you want to do it at 100 ms each. you may want to consider using an optoisolater as well between. solenoids can be noisy and mess with your uC or at least make sure you have good separation between the solenoids and uC. Why not just get one of the 40MHz dspic33fs? They're cheap and will give you some compute power as well. You haven't told us anything about your requirements or how big the solenoids are or anything. FETs tend to use less current, so I'd go with those over BJTs, note NFET vs PFET when considering which side of the solenoid you are planning on switching on, diodes in the right places are important too. Make sure to google for example circuits or you'll blow a few chips finding out the hard way.

 

[Tunelabguy]

...and if you use a shift register you better do some calculations, especially if it is 120, and you want to do it at 100 ms each.

Even a fairly slow 8 MHz PIC can pump out 120 bits into a shift register in about 300 microseconds.

 

[darkgnat]

I was thinking more future expansion, an excellent bonus for a $1-2 budget increase.