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→Components: Props to N0RC for pointing out U15 is a 555. Updated.
U14 - [http://web.archive.org/web/20200214042837/http://www.ti.com/lit/ds/symlink/cd74hc4051.pdf CD74HC4051PWR]
U15 - 92JK [https://www.ti.com/lit/ds/symlink/lmc555.pdf TI LMC555CMM Family] per the ZC5 (can't find much on this component)marking noted in datasheet. Pinout and footprint matches.
[[File:Screenshot 20200904-195417.png|thumb|92JK ZC5 chip noted as U15]]
{| class="wikitable"
|-
|3
|Trigger
|Rounded square wave (maybe sawtooth) alternating between 2msec and 4msec, resting at +3VDC between bursts
|-
|4
|Discharge
|Rounded square wave alternating between 3msec and 5msec, short periods of 0v, resting at +3VDC between bursts
|-
|5
|Output
|Data. Square wave. 5V space, 0v mark? Pulses around 250msec per bit.
|-
|6
|Threshold
|More rounded square wave bursts
|-
|7
|5VDCReset
|
|-
|8
|3.3VDCControl
|
|}
==Circuits==
=== RF Transmitter Circuit ===
The transmitter RF path contains a filter IC, pi matching network, broadband amplifier, and a few more output filter stages.
[[File:LMS6.png|alt=Schematic diagram|center|frameless|1065x1065px|Basic schematic of TX circuit on LMS6]]
U16 -Input also has a cap to ground not shown on the sketch.<br />
== Modifications ==
=== Disable amplification ===
When testing, it's important not to transmit on unlicensed frequencies. Emissions can be eliminated by removing the RF amplifier from the chain and terminating the load at the antenna connection. The amplifier is an SOT-89 device just above the "-" terminal of B3. To access this RF chain, the shield housing may need to be temporarily removed. Also remove the bias feed resistor just below the "L104" marking. Then, remove the transmitter antenna from the "ANT1" connections. Use a 50 ohm resistor across the two terminals to provide a terminating load and eliminate any further transmission. Near-field reception is still possible after making these changes.
