FREE 74HCT4351 to anyone who will use it for a cool idea
pedward
Posts: 1,642
I have a couple of reels of 74hct4351 8 way analog multiplexers. I will send 10 chips via USPS to anyone who comes up with a cool use, and will use them. The datasheet is attached.
Comments
Not looking for free hardware. I have enough stuff already.
The propeller can do 2 channels with 3 pins, so 4 COGs and 12 pins for straight S~D ADC, but certainly not efficient.
The HCT can run up to 10vdc and the Vee input is the analog ground, so you could run +-5vdc into these. They will run from 2 to 10v, so they are 3.3v compliant.
The /LE pin latches an input, otherwise it's transparent, this has the benefit of both being transparent and allowing you to snapshot an analog value and oversample it.
I was also thinking you could make a Logic analyzer with this, connect and sequence through all of the pins at high speed. You could use 2 timers, 1 to drive the selector through a 3 bit counter, then the other to gate the data input. You would use the same method Kurenoko(sp?) used in his 20Mbps (14Mbps) serial data comms.
If you had 4, you could sample 32 bits at > 10Mhz, but where to store the data???
Since these are bidirectional, you could also use it to fanout data on 8 lines from 1 input...or to inject data onto a bus.
The 74HCT4351 requires a 5V supply.
A good application for this chip(s) could be in touch sense pads on a pcb.
I have too many projects on the go now to do anything but this app note may help someone http://ww1.microchip.com/downloads/en/AppNotes/01102a.pdf
Shoot me, HC is 2-10v and HCT is 4.5-5.5v with a Vcc-Vee up to 10v. Anyway it would still work with the Prop.
The /LE pin is the Latch enable for latching the result on the common pin. when /LE is not latched the common pin sees the selected input in realtime.
Am I not understanding the Datasheet correctly?
Latch Enable manages the selected channel, not the voltage on the channel. When /LE is low (and enables properly set), any change on the Mux Select S[0:2] will not affect the selected I/O. Selected I/O can only be changed when /LE is high. See notes on page 4.
The S2 uses two 8 channel muliplexers to measure voltages on 16 lines. I think one of the multiplexers has an inverter on the enable pin so when one chip is enabled the other one is off. So you get double the channels at the cost of one additional Prop pin.