X-Git-Url: http://challenge-bot.com/repos/?p=challenge-bot;a=blobdiff_plain;f=pcb%2Freset_notes.txt;fp=pcb%2Freset_notes.txt;h=87a61a8789e2280ae52e1caf66bd74b49bbd8092;hp=0000000000000000000000000000000000000000;hb=468dbff97d0f5e6014495833ac23cab18c5e4eeb;hpb=f2a874c1149aca85083703362e435599ae211736

diff --git a/pcb/reset_notes.txt b/pcb/reset_notes.txt
new file mode 100644
index 0000000..87a61a8
--- /dev/null
+++ b/pcb/reset_notes.txt
@@ -0,0 +1,68 @@
+Patches:
+
+1) Swap U1 Vin/Vout -- 3 cuts + 3 wires
+
+Notes:
+
+1) U1 Vin/Vout pins are swapped
+2) Add a reset circuit
+
+Use a SNLVC2G06 (dual open collector inverter):
+
+At VCC = 5V:
+
+   VIH = .7 * VCC = 3.5V
+   VIL = .3 * VCC = 1.5V
+   VOL = .55V
+   IOL = 32mA
+
+Assuming that the capacitor is clamped to VOL most
+of the time, the R*C that corresponds to charging
+from VOL to VIH in T seconds:
+
+The basic capacitor charging equation:
+
+  V(t) = VOL + (VCC - VOL) * (1 - e(-t/R*C))			(1)
+
+Replacing V(t) with VIH and T:
+
+  VIH = VOL + (VCC - VOL) * (1 - e(-T/R*C))			(2)
+
+Solving for RC:
+
+  (VIH - VOL)/(VCC - VOL) = 1 - e(-T/R*C))			(3)
+
+  e(-T/R*C) = 1 - (VIH - VOL)/(VCC - VOL)			(4)
+
+  -T/R*C = ln(1 - (VIH - VOL)/(VCC - VOL))			(5)
+
+  R*C = -T/ln(1 - (VIH - VOL)/(VCC - VOL))			(6)
+
+Substituting in for T=1ms, VIH, VOL, and VCC:
+
+  R*C =  -.001/ln(1 - (3.5 - .55)/(5 - .55))			(7)
+
+  R*C = -.001/-1.08744
+
+  R*C = .009196							(8)
+
+Setting C = .1uF
+
+  R = .009196 / .0000001 = 9196
+
+Using an R near 10K should do the trick:
+
+The maximum discharge current is IOL.  Use Ohm's law
+to determine determine discharge resistor:
+
+   V = I * R
+   R = V / I
+     = 5 / .032
+     = 156.25
+
+Setting Rdischarge = 180 should be good enough.
+
+The charge/discharge ratio is:
+
+  Rcharge/Rdischarge = 10K/180 = 55.5
+