From: Bdale Garbee <bdale@gag.com>
Date: Sat, 19 Apr 2025 19:04:50 +0000 (-0600)
Subject: document planned simplifications
X-Git-Tag: fab-v2p2~3
X-Git-Url: https://git.gag.com/?a=commitdiff_plain;h=06b5143824326eb963f27c6f6fd5322c3d348934;p=hw%2Fquantimotor

document planned simplifications
---

diff --git a/Notebook b/Notebook
index 0fa5c4e..7fc252b 100644
--- a/Notebook
+++ b/Notebook
@@ -349,3 +349,31 @@
   a resistor suitable for 3mV/V, and use a screw terminal strip to attach it
   so customers don't have to scare us with their (lack of) soldering skills.
 
+2025.04.19
+- let's stop pretending writing an AD7997 emulation for the LPC is useful. I
+  see no way to get sample timestamps in userspace from the ADS8688 without
+  modifying the driver (they're stored at "interrupt" time, but not exposed
+  to userspace?).  After some discussion with Keith, the only reason we have
+  both sense_batt and sense_pyro is to determine state of the SAFE/ARM
+  physical switch.  But with a spare comparator, we could do that differently
+  and feed an RPI GPIO that state info.  It's also obvious that R11 and R17
+  should not both be there, that doubles the continuity current just because
+  of a thoughtless copy/paste from telefireeight.  So ..
+
+	- remove R11
+	- change the value of R15 to something slightly higher
+	- connect sense_batt to U13 pin 2, the comparator - input
+	- connect sense_pyro to U13 pin 3, the comparator + input
+	- connect U13 pin 1, comparator output, to an unused RPI GPIO
+	- connect sense_batt to an ADS8688 input
+	- connect sense_1 to an ADS8688 input
+
+  This means we're using 4 of the 8 ADC inputs for 
+	chamber pressure
+	thrust
+	battery voltage
+	igniter continuity
+  leaving 4 available inputs for daughter cards, like a strand burner
+  interface board with another pressure sensor and 3 burn wires.
+
+