130
edits
Changes
Jump to navigation
Jump to search
m
----
Fix small formatting/spelling and add scope images
=====Si5351 Breakout=====
I ordered the board and when it arrived, I attached it to an arduino nano with 5v, GND, SCL and SDA (A4 and A5 on the nano). After programming the board and checking it with my new DSO, it showed 45.55 MHz as programmed using the aforementioned arduino and the Etherkit Si5351 example sketch. I removed the crystal from the LO circuit and attached the Si5351 CLK0 to the collector of Q4 as is done with the original crystal and also grounded the breakout board to the other crystal pad.
Initial tests show nerly nearly identical functionality from stock, even without tuning any filter components onboard. The receiver now responds to signals on 147.350 MHz, comfortably near the top of the 2 meter band.
With that, I taped the arduino and breakout board together, insulated, and hijacked power from the main LM7812 regulator to power it.
Pin 13 of the IC is the RC input which is fed by a 1.1MOhm resistor and a 1uF 35v tantalum capacitor. Cross referencing those values in the datasheet chart, we get a RC timebase of ~1Hz, though measuring via scope it shows the period to be 0.66Hz (1.5sec/cycle exactly). The confusing part is that with these figures, we get a cycle time of ~110 seconds, not 180. Still not super clear how this works.
<gallery>
File:Cdf_timer_rc_scope2.png|Wide view of the RC oscillator via pin
File:Cdf_timer_RC_scope.png|Decoder modules bottom side (mirrored to match top side)
</gallery>
At low values it seems to be pretty accurate (eg. 5 sec), but with my test of "180s" (8, 6, 5 and 4 high) yielded approximately 3m18s (almost 200s). Timing the stock setting gets 2m57s, or 177s.
<br />
==General Notes/Things to Watch Out For==
