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Aug 15, 2019, 06:32 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by vollrathd
................... superhetrodyne radio with vacuum tubes. And that was amazing at the time.
..................................
I remember them well. I seem to recall they used an intermediate frequency of 455 khz.
Does that sound right?
Last edited by Jim.Thompson; Aug 23, 2019 at 03:01 PM.
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Aug 15, 2019, 08:09 PM
Registered User
vollrathd's Avatar
Thread OP
Quote:
Originally Posted by Jim.Thompson
I remember them well. I see to recall they used an intermediate frequency of 455 khz.
Does that sound right?
Yeah, they did use 455 Khz.

I've still got an old Control Air Mule Mark II 27 Mhz single channel transistorized transmitter and receiver in my workshop. Its only command is a single pushbutton that causes a relay to pull in on its receiver. After all these 60 some years, both the transmitter and receiver and its relay still work!
Aug 23, 2019, 09:48 AM
Quadaholic
--Oz--'s Avatar
Quote:
Originally Posted by vollrathd
Yeah, they did use 455 Khz.

I've still got an old Control Air Mule Mark II 27 Mhz single channel transistorized transmitter and receiver in my workshop. Its only command is a single pushbutton that causes a relay to pull in on its receiver. After all these 60 some years, both the transmitter and receiver and its relay still work!
When I raced rc cars for 2 decades, there was 6 channels on the 27mhz band, three of them you could swap Tx/Rx crystals and you had new channels. T Rx crystal was half the Tx crystal freq. But the other 72/75mhz bands, the Rx crystal was 455khz less than the Tx crystal, so swapping did not work.

I used to take a pair of crystals to Cal-Crystals in Anaheim Ca, they would analyze them, you could select a different freq (close by) and they would make you a set for less than you could buy them. I would select a couple channels higher (above my band) to have my own channel, it was awesome.
Aug 23, 2019, 11:25 AM
ErskyTx Developer
Mike Blandford's Avatar
I find problems with the accuracy of "real time" operations on Arduinos when working at the microsecond level. The standard libraries often disable interrupts for sufficient time (micros() in particular) to upset/delay other software unless you are using "hardware assist" like timer capture or timer output compare.

I have a SBUS to PPM converter running on an Arduino Pro Mini. I provide my own functions for things like micros() and millis() that work without using interrupts. The 16 servo outputs are then driven by the only interrupt ever running.

The code is available here: https://github.com/MikeBland/SbusToPpm.

Mike
Sep 11, 2019, 09:42 AM
Quadaholic
--Oz--'s Avatar
Quote:
Originally Posted by vollrathd
who remembers those 8 inch floppy disks?

And, I also made a servo driver many years ago using that 555 IC.
After I quit Xerox at 17, I started working for Mitsubishi electronics on 8" FDD's, then 5.25, then 3", also monitors, printers, power supplies, then I got into PC motorboards and all the controller cards (video/HDD/etc), at that point, I loved digital, they were a great company.

555, I built quite a few projects with that little gem.

It's amazing what you get for $10, plus add a 320x480 TFT 3.5" touch screen lcd for another 10. Plus all the sensors and modules for it, so flexible.
https://www.ebay.com/itm/Integrated-...72.m2749.l2649

But,,,,I feel like the twilight zone episode where the guy breaks his glasses and he cant read books w/o them, doh! (I am not a programmer)
Sep 11, 2019, 09:51 AM
Registered User
vollrathd's Avatar
Thread OP
Quote:
Originally Posted by --Oz--

It's amazing what you get for $10, plus add a 320x480 TFT 3.5" touch screen lcd for another 10. Plus all the sensors and modules for it, so flexible.
Yeah, Way back when, I bought a CK722 transistor for $7.50, putting a pair of them into a crystal radio I'd built. It made driving dad's farm tractor a bit easier.

FYI, at that time, a gallon of diesel fuel for that tractor was 18 cents. In today's dollars, that transistor would be over $100.
Sep 11, 2019, 10:15 AM
AndyKunz's Avatar
Quote:
Originally Posted by vollrathd
... that transistor would be over $100.
Actually, they're only about $40.

Andy
Sep 11, 2019, 10:53 AM
Registered User
vollrathd's Avatar
Thread OP
Quote:
Originally Posted by AndyKunz
Actually, they're only about $40.

Andy
Hi Andy, yeah I've seen those ads.

For other readers of this thread, if you blew up the diameter of each "transistor" in a 128 Gb SD memory card to the diameter of a human hair, it would cover several thousand square feet.

Now days, those old CK722's are so leaky, we'd call them defective.
Sep 11, 2019, 12:25 PM
AndyKunz's Avatar
I'm sure Bob Pease could come up with an application where the leakiness would work to our advantage. Sure do miss his column.

Andy
Sep 12, 2019, 12:07 AM
Quadaholic
--Oz--'s Avatar
Quote:
Originally Posted by AndyKunz
I'm sure Bob Pease could come up with an application where the leakiness would work to our advantage. Sure do miss his column.

Andy
I have heard that name before, but forgot what/where? Quick clue me in? Is he RIP now or?

Modern processors with the high clock freq and the amount of transistors are crazy, and now GaN is hitting the market.
Sep 12, 2019, 08:15 AM
AndyKunz's Avatar
He died a few years back in a car accident, on his way home from a memorial service for another great man.

He had a column in one of the EE mags entitled "Pease Porridge" and he'd answer questions from all over, in detail, explaining how to get the most from a circuit, or how to best select a component. A brilliant man, and super personable.

https://www.edn.com/electronics-blog...d-in-car-crash

He drove a VW Bug that was like 100 years old. He did all the maintenance on it as well, and was happy to brag about it.

Andy
Sep 25, 2019, 09:32 AM
Quadaholic
--Oz--'s Avatar
Thanks Andy!
That brings back old memories! RIP Bob.
Sep 25, 2019, 03:08 PM
Registered User
GeoffS's Avatar
Quote:
Originally Posted by Mike Blandford
I find problems with the accuracy of "real time" operations on Arduinos when working at the microsecond level. The standard libraries often disable interrupts for sufficient time ... I provide my own functions for things like micros() and millis() that work without using interrupts. The 16 servo outputs are then driven by the only interrupt ever running. ...
Yeah, that's the only approach that works at all for precise timing.

It seems I'm using that approach more and more for anything but very basic Arduino programs.
Sep 25, 2019, 06:55 PM
Registered User
vollrathd's Avatar
Thread OP
Quote:
Originally Posted by GeoffS
Yeah, that's the only approach that works at all for precise timing.

It seems I'm using that approach more and more for anything but very basic Arduino programs.
Arduino's are not alone in that respect. I've run into the same issues with those MicroChip PicChips when dealing with sub millisecond time routines. I'm using the mikroC software for the PicChips.
Sep 25, 2019, 11:37 PM
Registered User
GeoffS's Avatar
Quote:
Originally Posted by vollrathd
Arduino's are not alone in that respect. I've run into the same issues with those MicroChip PicChips when dealing with sub millisecond time routines. I'm using the mikroC software for the PicChips.
Aside: Strangely enough on most single-core CPUs, the fastest way to read a port (ex. an ADC) is not to use interrupts but rather a super-tight polling loop like the pseudo-code below.

The maximum delay for this code (i.e. between when the "valueReady" bit is raised and the value is read and stored) is about 10 instructions (give or take).
On a 16 MHz one-instruction-per-cycle CPU that's 62.5 ns/instruction * 10 instructions = 625 ns
The interrupt latency (i.e. between the time the external flag is raised to reading the value) on many (most?) machines is usually on the order of 100+ instructions.

The downside is that you can't do *anything* else while the data-acquisition is running.

Code:
int i = 0;
bool notDone = true;
while(notDone)
{
    if(valueReady)
    {
        dataArray[i++] = readValueFromPort;
        if( i > totalNumberOfPointsToRead) notDone = false;
        while(valueReady) {}  // Wait for the external flag to drop.
    }
}
I used this technique a number of years ago (8 MHz 68000) when I needed to read values from an ADC at a rate much faster than the interrupt latency of the 68000.


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