little circuit problem

Maybe this is naive, but why not just put a red-green LED across the rosa signals? That way you have red (off), green (on), and yellow (toggling) options. You could AC-couple one of the directions to get off/green/yellow or maybe off/green/red.

The next simplest circuit... is a pair of tiny PICs talking serial over that link. Two chips :-)

The CML rosa sigs are too weak to drive LEDs directly, and are AC coupled. These telecom links seem to not work well below about 1 MHz.

I don't think the ac-coupled links would send async ascii-type signals. They could send square waves of various frequencies, or dc-balanced NRZ or biphase or 8B10B data.

Someone here has suggested using a small FPGA in, at least, the T box. But that needs design and per-unit programming somehow. The upside is that we could probably feed the rosa CML outputs directly into some FPGA differential input.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Hmmm... could they be made compatible with a CANbus tranceiver? That still implies MCU, plus the two CAN chips, but it's another option...

(or some other off-the-shelf tranceiver, like LVD-to-ttl)

or a serdes? You could wire up some of the parallel inputs of the serdes so that it always makes AC.

I'm thinking that an R box could send a square wave back to T. 1 MHz means "I'm here" and 4 MHz means "I'm getting your data." That's some simple oscillator with one TTL input from the signal detector. (The other bit of the 3-state code is just Vcc.)

The T box now needs a discriminator for each return channel, driving two LEDs.

It's a not-too-critical but cute problem to come up with minimal circuits to do this.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

On a sunny day (Thu, 09 May 2019 21:23:23 -0700) it happened John Larkin wrote in :

4046 freq too low PC output high, freq too high PC output low sort of thing, 2 LEDs on that pin. No signal at all maybe both light (would have to try that)? You can use it to make the frequencies too.

4046 freq too low PC output high, freq too high PC output low sort of thing, 2 LEDs on that pin. No signal at all maybe both light (would have to try that)? You can use it to make the frequencies too.

PS come to Sink of it: one 4046 as FM mod at say 1 Mhz on the Tx side, the other as FM demod PLL on the Rx side. Now you can send any digital serial data you want, or you can use a EPROM at the Tx side with a 4040 counter and R2R network to say: 'I am number one and things are OK here', etc, 'I am number two and am overheated' and an audio amp on the Rx side with a small or BIG speaker.

Its easy, have done that, FM link with 4046. PIC would work too, but programming,....

I'd forgotten all about the 4046... haven't used one in decades. The transmit end (in an R box) could just use the VCO part. The HC4046 can do up to 24 MHz at 3.3 volts.

As the receiver in the T box, the pll dc output could drive two comparitors to light my two LEDs.

I was also considering a tachometer circuit, an HC123 one-shot and a lowpass RC, to convert frequency to DC voltage, into that same dual comparator. HC123 is a dual, so that's a slight simplification.

The receiver still needs a converter from the rosa's CML diff output to TTL. I guess that can't be avoided.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

In homage (apply French accent) to your graphic style, I submit as the receiver and LED driver

which accepts the wimpy CML directly. If the transmitter is a 4046 VCO, the two frequencies can be whatever works best.

Oh, add a resistor to ground on the lower comparator input.

Adding two schottky diodes, comparator inputs to ground, would be interesting. That allows cheap slow comparators to be used.

Too tricky maybe. I'm thinking HC4046 at the send end and the HC123 tachometer thing at the receiver. Just do the CML to TTL.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

You could simplify two leds down to one. Off = no connection; solid-on = connected; Flickering-on = connected and data traffic.

piglet

On a sunny day (Fri, 10 May 2019 08:26:59 -0700) it happened John Larkin wrote in :

Yes, had to look at your 'graphics' for a while, you use Q of LC to get high voltage on C to bottom comparator for 4 MHz. But you may have a logic problem, would need 2 tuned circuits, one for each frequency?

Yes 74HC123 could work, has only 5 pF input capacitance. Maybe sensitive to noise, false triggering.

4046 PLL and comparators on the control voltage should also work.

Will think about it :-)

DTMF encoder - and decoder chips come to mind too, could be cheap, but those use audio range frequencies, gives you more bits though. Could use FM and the 4046 PLL to send and demodulate those frequencies.

I am sure there are many other possibilities

The LED states are: both off, one on, and both on. The LINK led should light if any frequency is coming back from an R box. The DATA led should light only on 4 MHz.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

On a sunny day (Fri, 10 May 2019 11:37:07 -0700) it happened John Larkin wrote in :

Ok, got it.

I just checked ebay for DTMF encoder and decoder chips, the generators are about 29 cent:

The receivers about 47 cent:

Saves a lot of tinkering and is an universal system... 4 bits out. Press 1, 2, 4, 8 (MOSFET in Tx side as key switch) for 4 LEDs?

The fiber links are AC coupled and some are useless below 1 MHz, so I need to go fast.

HC4046 is 22 cents. Good suggestion.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Here's a CML (or ECL) to TTL converter for about 7 cents. That can drive my HC123 tachometer, which can drive a dual comparator to light the LEDs at 1MHz and 4MHz. 45 cents total maybe.

The FSK tx end is your 4046, another 40 cents maybe.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

In the spirit of gray on gray sketches here is mine:

The Mhz oscillator is gated off at a few Hz if there is a stream of data pulses. Everything is AC coupled so a stuck high/ stuck low fault is apparent.

The 50ms blink-on blink-off half shots could probably be tidied up into a 74HC123

piglet

Interesting. But the light pipes come in twos, and we'd have to explain the single-LED blink patterns to the users. The two LEDs can be LINK and DATA which is arguably clear in meaning. Maybe.

The data seen at the recever is GHz stuff, so that needs a separate detector that supplies a TTL level to this link. That will already drive a local DATA led on the R box.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

No problem. I saw the network activity light on my modem/router which indicates the same kind of thing: disconnect, connect, active.

You asked for simple and I enjoyed the challenge.

piglet

The collector cap needs a resistor though.

NT