RTTY demodulator using NJM2211 - Revision history

Morris at 08:07, 17 January 2012

2012-01-17T08:07:08Z

Morris at 06:22, 17 January 2012

2012-01-17T06:22:29Z

Morris at 06:21, 17 January 2012

2012-01-17T06:21:54Z

Morris at 23:33, 8 August 2011

2011-08-08T23:33:11Z

Morris at 00:39, 7 August 2011

2011-08-07T00:39:52Z

Morris at 19:49, 3 August 2011

2011-08-03T19:49:40Z

Morris at 19:49, 3 August 2011

2011-08-03T19:49:22Z

Morris at 19:47, 3 August 2011

2011-08-03T19:47:59Z

Morris at 19:38, 3 August 2011

2011-08-03T19:38:20Z

Morris at 19:37, 3 August 2011

2011-08-03T19:37:46Z

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 The board is a straightforward application of the NJM2211 FSK decoder chip. It accepts an audio signal and decodes it into on and off keying of a teletype current loop circuit via an optical isolator which protects your computer or radio from the high voltage and inductive spikes on the loop. It has the additional feature that when it's not locked on to a signal, it keeps the the loop closed so that the attached teletype machines won't "run open."
-The board was designed to be cheap and small, and as such it does not include various bells and whistles such as the ability to invert mark and space. As is, it will correctly decode the ITTY signal, and if you're getting audio from a radio, it's probably a sideband receiver where you can switch to the opposite sideband, which achieves the same thing. The board does not provide the loop current – like a keyboard or tape reader, it just makes and breaks the existing circuit. The output can handle 60 or 20mA loop and is safe to 200 volts. There's been discussion on the Greenkeys mailing list about how to make a loop supply, if you need one.
+The board was designed to cost $20, and as such it does not include various bells and whistles such as the ability to invert mark and space. As is, it will correctly decode the ITTY signal, and if you're getting audio from a radio, it's probably a sideband receiver where you can switch to the opposite sideband, which achieves the same thing. The board does not provide the loop current – like a keyboard or tape reader, it just makes and breaks the existing circuit. The output can handle 60 or 20mA loop and is safe to 200 volts. There's been discussion on the Greenkeys mailing list about how to make a loop supply, if you need one.
 George Hutchison W7TTY's excellent ITTY service can be found at http://rtty.com and is a perfect source of AFSK data for this board. In addition, there are many web-accessible software defined radios available to the public. An index of them can be found at http://websdr.org – choose one, find a signal, plug your computer's audio output into this board, and watch your machine print the traffic!

← Older revision		Revision as of 06:22, 17 January 2012
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−	The board is a straightforward application of the NJM2211 FSK decoder chip. It accepts an audio signal and decodes it into on and off keying of a teletype current loop circuit via an optical isolator which protects your computer or radio from the high voltage and inductive spikes on the loop. It has the additional feature that when it's not locked on to a signal, it keeps the the loop closed so that the attached teletype machines won't "run open" ~~noisily printing gibberish.~~	+	The board is a straightforward application of the NJM2211 FSK decoder chip. It accepts an audio signal and decodes it into on and off keying of a teletype current loop circuit via an optical isolator which protects your computer or radio from the high voltage and inductive spikes on the loop. It has the additional feature that when it's not locked on to a signal, it keeps the the loop closed so that the attached teletype machines won't "run open."

	The board was designed to be cheap and small, and as such it does not include various bells and whistles such as the ability to invert mark and space. As is, it will correctly decode the ITTY signal, and if you're getting audio from a radio, it's probably a sideband receiver where you can switch to the opposite sideband, which achieves the same thing. The board does not provide the loop current – like a keyboard or tape reader, it just makes and breaks the existing circuit. The output can handle 60 or 20mA loop and is safe to 200 volts. There's been discussion on the Greenkeys mailing list about how to make a loop supply, if you need one.		The board was designed to be cheap and small, and as such it does not include various bells and whistles such as the ability to invert mark and space. As is, it will correctly decode the ITTY signal, and if you're getting audio from a radio, it's probably a sideband receiver where you can switch to the opposite sideband, which achieves the same thing. The board does not provide the loop current – like a keyboard or tape reader, it just makes and breaks the existing circuit. The output can handle 60 or 20mA loop and is safe to 200 volts. There's been discussion on the Greenkeys mailing list about how to make a loop supply, if you need one.

← Older revision		Revision as of 06:21, 17 January 2012
Line 1:		Line 1:
−	The board is a straightforward application of the NJM2211 FSK decoder chip. It accepts an audio signal and decodes it into on and off keying of a teletype current loop circuit via an optical isolator which protects your computer or radio from the high voltage and inductive spikes on the loop. It has the additional feature that when it's not locked on to a signal, it keeps the the loop closed so that the attached teletype machines won't ~~clatter away or print~~ gibberish.	+	The board is a straightforward application of the NJM2211 FSK decoder chip. It accepts an audio signal and decodes it into on and off keying of a teletype current loop circuit via an optical isolator which protects your computer or radio from the high voltage and inductive spikes on the loop. It has the additional feature that when it's not locked on to a signal, it keeps the the loop closed so that the attached teletype machines won't "run open" noisily printing gibberish.

	The board was designed to be cheap and small, and as such it does not include various bells and whistles such as the ability to invert mark and space. As is, it will correctly decode the ITTY signal, and if you're getting audio from a radio, it's probably a sideband receiver where you can switch to the opposite sideband, which achieves the same thing. The board does not provide the loop current – like a keyboard or tape reader, it just makes and breaks the existing circuit. The output can handle 60 or 20mA loop and is safe to 200 volts. There's been discussion on the Greenkeys mailing list about how to make a loop supply, if you need one.		The board was designed to be cheap and small, and as such it does not include various bells and whistles such as the ability to invert mark and space. As is, it will correctly decode the ITTY signal, and if you're getting audio from a radio, it's probably a sideband receiver where you can switch to the opposite sideband, which achieves the same thing. The board does not provide the loop current – like a keyboard or tape reader, it just makes and breaks the existing circuit. The output can handle 60 or 20mA loop and is safe to 200 volts. There's been discussion on the Greenkeys mailing list about how to make a loop supply, if you need one.

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 [[File:rttydemod-sch.png|800px]]
 [[File:rttydemod-brd.png|290px]]
-<p>
 Notes.
 There are a number of optocoupler / solid-state relay parts that can work here. They vary in peak load voltage, current-handling capability, switching time, and input requirements. The current winner in terms of cost/performance is the PS7141E, which costs $1.57 at quantity 10-100:
 Measured values from sample part:
 LED forward current: 11 mA w/ 330 ohm series resistor - 13mW dissipation, max = 50mW. Closed output switch drops 2v @ 60mA = 120 mW (max = 560 mW continuous) - 33 ohms, right to spec. This isn't great, but not tragic on a 150v loop. For lower on-resistance, you pay more money, or use more components. At least it drops less than an actual selector magnet, and isn't inductive. Turn on time < 500uS, turn off time 70uS.

← Older revision		Revision as of 00:39, 7 August 2011
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	[[File:rttydemod-sch.png\|800px]]		[[File:rttydemod-sch.png\|800px]]
	[[File:rttydemod-brd.png\|290px]]		[[File:rttydemod-brd.png\|290px]]
		+	<p>
		+	Notes.
		+	There are a number of optocoupler / solid-state relay parts that can work here. They vary in peak load voltage, current-handling capability, switching time, and input requirements. The current winner in terms of cost/performance is the PS7141E, which costs $1.57 at quantity 10-100:
		+
		+	Measured values from sample part:
		+	LED forward current: 11 mA w/ 330 ohm series resistor - 13mW dissipation, max = 50mW. Closed output switch drops 2v @ 60mA = 120 mW (max = 560 mW continuous) - 33 ohms, right to spec. This isn't great, but not tragic on a 150v loop. For lower on-resistance, you pay more money, or use more components. At least it drops less than an actual selector magnet, and isn't inductive. Turn on time < 500uS, turn off time 70uS.

@@ Line 6: / Line 6: @@
 The instruction sheet shipped with the boards can be found here: [[Media:rttydemod-instructions.pdf|instruction sheet]]
-The latest parts list is here: [[Media:rttydemod-bom.txt|BOM]]
+The latest (very rough) parts list is here: [[Media:rttydemod-bom.txt|BOM]]
 <p>
 [[File:rttydemod-sch.png|800px]]
 [[File:rttydemod-brd.png|290px]]