RLC-1 RS232 Level Converter in a DB9 backshell

Ashley Roll has put together a really nice little unit here. Leave off the MAX232 and keep these handy for the few times you need true RS232! Plugs into any 0.1" header to connect to your circuit. Perfect for the BASIC Stamp or other microcontroller appications.

User comments:

Brady Palmquist says: "James...got your RS232/TTL cable today. FAST! And it looks great. Will work great for programming radios. Thanks VERY much."

Erik Hanson reports that with a little modification, the RLC-1 can be made into an ECS port converter cable for data sent by the Sony DAS (Digital Alignment Software) to control all aspects of the operation of the monitor. The RLC-1 must be modified by re-arranging the pins in the socket to match those on the monitor. The pinout of the connector is, from top to bottom:

GND (The RLC1 has +5V here, so swap pins 1 and 2)
+5V (The RLC1 has GND here, so swap pins 1 and 2)
Rx (The RLC1 Tx pin is in the correct place aready to send data to Rx on the monitor)
Tx (The RLC1 Tx pin is in the correct place aready to send data to Rx on the monitor)

We now have an ECS specific version of the RLC1 (called the RLC2) which had the correct pinout and a longer cable. It's the same other than that; if we are out of stock on RLC1's and you are in a hurry, order an RLC2 and swap pins 1 and 2.

Also:

RS-232 / I²C-Adapter & Parallel I/O Module

Shown With Backshell removed

RLC-1 Datasheet

Digital Nemesis Pty Ltd
www.digitalnemesis.com

Introduction

The RLC-1 RS232 to 3-Volt or 5-Volt (CMOS/TTL) Level converter provides a simple, low-cost and easy to use solution to interfacing a CMOS or TTL based circuit to an RS232/EIA232 serial port.

The RLC-1 contains an internal circuit to provide the positive and negative voltages needed for true RS232/EIA232 compatibility and to convert these voltages back to logic levels.

It is particularly suited to micro-controller applications; for instance the PIC or ATMEL families of devices and products using these.

The RLC-1 is built into a small DB9 backshell with a short (10cm or 4") lead terminating in a standard 0.1" (2.54mm) Molex KK-series 6 pin connector. The connector is used to provide power to the converter and deliver the Serial data signals to the attached circuit.

Its small size and convenience make it ideal for prototype or one-off systems, eliminating the need to design and debug extra level shifting circuits. It is also useful for circuits that need periodic connection to a host like dataloggers where a single converter can be used with many products, reducing the parts count and therefore cost for the individual units.

Connections

Logic Level Pin Assignments

Pin	Color	Signal	Description
1	WHT	Vcc	Power supply to the RLC-1. 3 to 5 Volts.
2	BLK	Gnd	Ground Connection (0V).
3	RED	Data Out (TX)	Data sent from the logic level device to the RS232 device.
4	GRN	Data In (RX)	Data sent from the RS232 device to the logic level device.
5	BRN	RTS	Request to Send signal sent from the RS232 device to the logic level device to indicate it wishes to transmit data. This signal is Active Low.
6	BLU	CTS	Clear to Send signal sent from the logic level device to the RS232 device indicating that it can begin sending data. This signal is Active Low.

Logic Level Interface
The logic level (CMOS and TTL compatible) interface is a Molex KK Series, locking and polarised 6 pin crimp terminal housing. A compatible header for these connectors should be available from most electronics stores, alternatively a 0.1" (2.54mm) universal header could be used.

Note that the logic level interface is not isolated from the RS232 level interface and they share a common Ground.

RS232 Interface
The RLC-1 is build into a DB9 Backshell and comes with a female DB9 connector.

The DB9 RS232 connector is wire as a standard "Null Modem"; DTR, DSR and CD are permanently wired together but the RTS and CTS signals are provided to the 5-Volt interface and must be connected together if not used in the attached circuit.

Specifications

Symbol	Parameter	Conditions	Value			Unit
Symbol	Parameter	Conditions	Min	Typ	Max	Unit
I_supply	V_cc Power Supply Current	No Load, T_A = 25 Deg C		0.3	1	mA
V_IL	Logic Level Input Threshold Low				0.8	V
V_IH	Logic Level Input Threshold High		2			V
V_OL	Logic Level Output Voltage Low	I_out = 1.6mA (to V_cc)			0.4	V
V_OH	Logic Level Output Voltage High	I_out = 1mA (to Gnd)	V_cc-0.6	V_cc-0.1		V
D_R	Data Rate		300	400		Kbps

Electrical Characteristics:
V_cc = 5V +/-10%, T_A = -40 to 85 Deg C, unless otherwise specified. Typical Values are referred to T_A = 25 Deg C.

Absolute Maximum Ratings:
Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not to be implied.

Symbol	Parameter	Value	Unit	Notes
V_cc	Unit Power Supply	-0.3 to 6	V	Relative to Ground
V_Dout	Input Voltage on Data Out Connection	-0.3 to (Vcc +0.3)	V	Relative to Ground
V_Din	Output Voltage on Data In Connection	-0.3 to (Vcc +0.3)	V	Relative to Ground
T_Store	Storage Temperature Range	-55 to +125	°C

Options Available

Digital Nemesis Pty Ltd makes a single standard unit, but is able to adapt them as needed. Note that a minimum order quantity will apply for non-standard configurations. For more information, please contact SPAMsales at spamdigitalnemesis.com.

The following are some of the available options: (all units now support 3 Volt as well as 5 Volt operation)

Rugged All Metal Backshell
No Backshell
Bare Leads for Logic Level Interface
Custom Connector for Logic Level Interface
RTS and CTS internally connected and a 4 Pin connector for the Logic Level Interface

Questions:

Arthur asks: "Does the RCL invert the Pin-3 data out signal?" James Newton answers: "Yes, the signal is inverted in terms of electrical polarity. e.g. a TTL low will generate a positive voltage on the TX output pin, a TTL high will generate a negative TX. But the other possible correct answer is No, the signal is not inverted in terms of logic. In the RS232 standard, a low electrical level (–3 to –15 volts) is defined as a logic 1, or 'on' or 'high' and is referred to as 'marking.' So a TTL high, will generate an RS232 high.

Comments:

"On the page http://www.piclist.com/techref/io/serial/RCL1.htm, it starts with "RCL" and becomes "RLC" throughout the rest of description. Yep, I know: Picky, Picky, Picky!!! Thanks for an interesting and useful site." +James Newton answers: "Oops."

See also:

http://www.awce.com/rs1.htm Kit with larger components. Does not include a cable. 5 Volt operation only. As of 2006/08/03 the cost was $10 for the PCB only, $14 for the kit and $26 A&T. If you don't mind the size and want to save $5 in return for building the kit, this is a good option.
http://www.dontronics-shop.com/RLC-1-RS232-to-5-Volt-Level-converter-p-16186.html Another source for the RLC-1. As of 2008/02/05 the price is $26 USD. It may be a better option for people ordering outside the USA depending on the shipping.
http://www.embedinc.com/products/ser Larger, no case, no cable, does not convert RTS or DTS, does not support 3.3v. Ss of 2008/02/05 the price is one dollar less up to qty 4, but the 5 unit price is $13.80 which is quite good.
CoolMCU Converter Cable. Physically larger than the RLC-1. Used to sell a version that was not a true MAX232, but the current version seems like a good product. From Canada, so expect shipping and customs delays. Priced at $16 plus $11 express shipping to US (5 to 7 business days advertised) for a total price of $27. Compare with our $21 + $6 for 2-4 day Priority Mail shipping. The price is the same, the shipping is faster. Read the ebay comments: Many times shipping is fast, but you may be the one that gets held up in customs. "Product works great, but it took over three weeks for me to receive it (USA)." kielziz( 5 ) Jun-01-06 08:21 "Works as described. Shipping is a little slow." asylumboy( 4 ) Jun-01-06 08:10 and so on. In the end, the same thing costs less in Canada, but more to ship to the USA. I have offered to resell this product in the USA, but he is apparently not interested.
http://www.ipenabled.com/ttl-rs232.html Almost $100 with power supply and shipping.
http://www.superdroidrobots.com/shop/category.asp?catid=41 $10 more but has a longer cable. I personally would not think that a TTL signal would be reliable at higher speeds over a cable that long.

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Quick, and RELIABLE! RCL-1 RS232 Level Converter in a DB9 backshell only $15.00
Ashley Roll has put together a really nice little unit here. Leave off the MAX232 and keep these handy for the few times you need true RS232!