Custom Products from Masters Communications

Description:
The CSM-32S is a very small CTCSS encoder/decoder on a single printed circuit board. For those familiar, it's approximately the same size as a Com-Spec TS-32. Connection to the board is made with a female DuPont connector to an 11 pin male header. There are two male header connector options available depending on your monting requirements. A (vertical) straight header is best where height is not constrained. The (horizontal) angle header adds more area, but minimizes the height to that of the parts on the board. A third option is no header where you install your own wires into the holes in the circuit board. An 11 pin DuPont connector with mating female (socket) pins are included with either header option.

Upon decoding a valid CTCSS tone, the board gives a logic change. Both active high and active low outputs are available simultaneously. A MX-465DW CTCSS chip is used for CTCSS tone generation, detection, and audio filtering. This chip is not duplex - meaning it will not generate (encode) and decode simultaneously. Kits are supplied with the large surface mount chip and tone selection switch preinstalled, but other surface mount components do exist. This kit is intended for experienced builders that have surface mount installation confidence using a standard low-wattage soldering iron.

Why do we need this board?
Not all radios have easy access to quality CTCSS logic signals.   Some repeater hardware may not include CTCSS generation or detection or may require reprogramming just to change the CTCSS tone frequency.   The Com-Spec TS products are great, but they are no longer availalable new, and the audio filter in them leaves a lot to be desired. The filtering properties of the CSM-32S are superior in response, group delay, and depth. CTCSS tone generation (encode) provides over 2V P-P of audio, and is controlled in level with a small pot.

Operation:
There is one LED for status. It is red and indicates valid CTCSS tone detection.   The tone frequency is set by a DIP switch.   All of the functionality of the MX-465 is brought out to the edge of the board where the 11 pin connector installs.   The signals include the logic line to tell the chip to encode or decode, as well as all of the audio filter and discriminator audio input connection, and - of course, power and ground. There are two filters and muting that are available for the transmitter and receiver - in case someone wants to utilize them.

About the inputs and outputs:
There are only three necessary connections for operation as a decoder; buffered discriminator audio (pin 9),power (pin 3), and ground (pin 2).

The normal logic outputs are routed to the 11 pin connector. These outputs on pins 1 & 8 are not totem pole, however, separate logic outputs are available - - active high (pin 1) and active low (pin 8). There are also open collector outputs available from 2 holes marked A - B that are included on the circuit board. These outputs can be used for operations that are beyond the original scope of this board.

Tone Encode:
Tone generation additionally requires grounding the TX/RX mode select line (pin 4), and routing the encode audio (pin 10) to the transmitter. Tone encode level is controlled by a potentiometer VR1 - from 0 (zero - no output - CCW) to more than 2.0V P-P of encode audio into a 10k load impedance with VR1 set to its maximum (CW) rotational position.

Please see the Support Documentation article to understand all of this boards functionality including the audio filters and mute gates.

Features:

	Two header options are available, one is provided.   You choose which one - or choose none at all.
	11 position female DuPont connector housing and 12 mating socket pins included with header option to build your own interface cable. You supply the wires.
	Recommended Power Source: +7 to +16 VDC at 7mA standby and 20mA decoding. Must be constant, not switched.   Maximum is 24 VDC.
	Onboard regulation +5V for the MX465DW and logic.
	Board is 1.3 by 2.0 inches - the same size as a "TS-32".
	Tone Frequency is set by dip switch selection.
	Low current draw, about 7 mA standby and 20 mA with the LED lit, depending on logic sourced and its input impedance. (Measured at 13.8 VDC input)
	All logic is sourced from 5 VDC.   Pull-up and pull-down resistors are included on the normal logic outputs available at the header.
	Small size - can fit inside many radios.
	A pot is provided to set the encode level.
	Add a quality CTCSS encoder or decoder to a radio whose logic signals are hard to get to.
	Simple to hook up and set up. Requires a few hundred mV RMS of "raw" audio.
	90 day Limited Warranty.  Repair available for units out of, or not covered under, warranty (my determination).
	Mounts with double-sided foam tape (not included).
	Hookup is made with a mating 11 position female DuPont connector and contacts (both included). Or - solder wires directly to the holes in the circuit board for those truly confined spaces.
	Kits are supplied with the surface mount 24 pin IC and 6 position switch already soldered onto the board.
	Comes with surface mount and thru-hole components, and is only recommended for the experienced builder.

Click here for schematic, parts list, construction notes, installation, and set-up instructions.

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CSM-32S Unassembled Project Kit
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Support Documentation

Email Kevin Custer for ordering or support of this exciting product.
 

Product of Masters Communications, all rights reserved.
Specifications may change without notice.
Images are property of Kevin Custer - W3KKC
Original board layout by Kevin Custer - W3KKC
HTML August 12, 2025, W3KKC All Rights Reserved!