Micron RX S/C output

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John Ryan
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Joined: 31 Mar 2021, 03:56
Location: Rotorua New Zealand

Micron RX S/C output

Post by John Ryan »

Has anyone converted an old Micron RX to Single channel. Im still flying S/C with an RCS Mk3 Guidance system. And also have an OS Pixie that still works. Im now playing with a Futaba 35Mhz FM Tx module modulated with a 555 tone generator. I can hear the tone at the input of the 4017 decoder (pin14) in the Rx so I need some way to drive an escapement! I still have a couple of Elmic and OS escapements to have some fun with.
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Shaun
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Joined: 15 Feb 2018, 21:49
Location: West Yorkshire

Re: Micron RX S/C output

Post by Shaun »

Phil and Pete have both built 35mhz s/c sets in the past. I'm sure they'll offer some guidance when they see your post.

Shaun
Pchristy
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Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Micron RX S/C output

Post by Pchristy »

Assuming the Micron Rx uses a 3357 - or one of its clones - you can use the sync separator circuit as a tone detector.

From memory, the sync separator comprises a 0.1uF capacitor which charges up through a 47K resistor connected to the +ve supply. This is discharged via a 150 ohm resistor every time a pulse appears on the output pin14. During the "pulse" sequence, the voltage on the 0.1uF never gets high enough to store a "1" on the input of the shift register decoder. During the sync pause, the charge rises enough to store the "1", the discharge being slowed by the 150 ohm resistor.

Instead of connecting the junction of the 0.1uF and 47K to the decoder i/c, connect it to pin 10 of the 3357 via another 47K resistor. Pin 10 is the input of a very high gain amplifier, which will act as a level detector for the voltage on the 0.1uF capacitor. The output of the amp is on pin 11, and will change state in the presence or absence of a tone.

You will need to add some kind of switching transistor, driven by pin 11, to handle the current requirements of an escapement. I used a pair of ZTX451 arranged as a Darlington pair, to provide the output for an Elmic escapement.

In fact, I used a complimentary pair of ZTX550 (PNP equivalent of the ZTX451) arranged as a "Totem pole" output stage to provide a pulse proportional output to a centre tapped battery if required.

If I can find my s/c circuit diagram, I'll post it. It may be a bit tatty with age, and I'll have to find it first and scan it...

UPDATE: I'm attaching both my single-channel Rx circuit, and a multi-channel one I did for Roy Lever as a comparison. Both heavily based on the RCM&E Rx, but I use a Toko 10420 as the receiver IC. This is pin compatible with the 3357, but seems to have a better overload tolerance!

--
Pete
Attachments
SC_rx.pdf
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Lever_rx.pdf
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John Ryan
Posts: 36
Joined: 31 Mar 2021, 03:56
Location: Rotorua New Zealand

Re: Micron RX S/C output

Post by John Ryan »

Many thanks for your help I'll give that a go.
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Phil_G
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Re: Micron RX S/C output

Post by Phil_G »

HI John, sorry for the late response, domestic problems mean I'm not around much lately... Image
I used half a Micron in my 35Mhz S/C receiver:




The add-on switcher board is very simple, just a small MOSFET, a 0.1uF cap and a 100kΩ resistor:


micron_mod.jpg


The MOSFET is an 2SK1112 but isnt critical, its what I had at the time. I see they've become expensive so an IRF110 should do and is much cheaper:
https://uk.rs-online.com/web/p/mosfets/1451621/ ...any N channel mosfet with Rds under half an ohm and a gate threshold of 2v ish.
Other than removing the decoder, the Micron receiver is unmodified, the white wire carries the PPM signal and when it rests during the sync pause, the FET is switched on. Its very simple but works perfectly and the Micron is an excellent receiver. I've shown white as yellow in the diagram, I dont know if the PPM wire is white on all Microns, but its the only other wire apart from pos & neg. The combined rx and switcher is powered from a 4 cell NiMh or in my case a single lipo cell - note that the battery wires also connect to the red/black from the receiver - ie they're soldered to the same veroboard rails as the red/black from the receiver, as can be seen in the photos:


IMG_20210501_120758.jpg

IMG_20210501_105526.jpg

IMG_20210501_105635.jpg


The transmitter is an ordinary, unmodified Hitec HPF-MI as used in the Optic 6 and by Frank & myself in several conversions.
The PPM input is driven by a 1khz squarewave keyed by the button - normally 'on' in my case (see the video). If you imagine a PPM pulse train without any sync pauses, its just a continuous stream of square wave pulses, which is what we have here. At the receiver, there is no sync so the sync-detector doesnt trip until you press the button, when it detects the sudden lack of pulses and switches the MOSFET, operating the escapement coil.
The combination of a HItec RF module and a proven receiver makes the creation of a genuine 35Mhz S/C tone set very easy Image

Hope this helps
Cheers
Phil
John Ryan
Posts: 36
Joined: 31 Mar 2021, 03:56
Location: Rotorua New Zealand

Re: Micron RX S/C output

Post by John Ryan »

Thanks Phil That makes for a very simple mod.
John Ryan
Posts: 36
Joined: 31 Mar 2021, 03:56
Location: Rotorua New Zealand

Re: Micron RX S/C output

Post by John Ryan »

Thanks to Phil I now have things working.
I wondered if using a P Fet channel would allow the escapement to pull in on tone. As I had one in the scrap bin I figured it was worth a try. After reversing the circuit it all worked. My Tx is running about a 600Hz tone so the escapement was rather noisy. By increasing the cap to 0.18mfd it settled down. My intention is to attach the switch to the Rx case so it can be used a S/C and regular Rx. Attached is diagram of the Rx complete with S/C switch and a couple of pix of the setup and also my RCS Tx running one of Phil's emulators on the back of a 40Mhz Futaba Tx module.

Having recently built the GG pulser (RCM&E Dec 1969) and having it driving a relay connected to a Rand LR3 successfully the next project is.
*Use my 35Mhz S/C tone Tx driven by the pulser.
*Use the Mini Micron Rx modified as above connected to an H bridge to drive the Rand.
Inside RCS Tx
Inside RCS Tx
RCS Tx
RCS Tx
Switch
Switch
Getting it to work
Getting it to work
Shingle_channel_Micron_mini.pdf
Circuit
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John Ryan
Posts: 36
Joined: 31 Mar 2021, 03:56
Location: Rotorua New Zealand

Re: Micron RX S/C output

Post by John Ryan »

A small correction. Connect the source of the FET to the battery positive supply. Not the emitter of the supply transistor. A high output current will fry it.
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Wavemeter
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Joined: 16 Feb 2018, 21:22

Re: Micron RX S/C output

Post by Wavemeter »

Well I’m so glad I came across this posting ! I cannot bear throwing away anything radio control that might be or could be restored to working condition. I have a Skyleader double deck superhet with a fried decoder board. Ok so the decoder I did throw ! I had been fiddling for weeks of evenings with a Darlington pair soldered to a relay . Marginal results . So seeing this prompted a scan of the RS page for the mosfet . ( link posted earlier ) But you need to buy so many of the little blighters . So I looked on Amazon and sure enough much smaller quantities available . Then I came across this:

https://www.amazon.co.uk/gp/aw/d/B06XB9B16Z?psc=1&ref=

It’s a MOSFET switcher designed for an Arduino. £3:99 plug and play . Do I did ! And it works! Yet to put a load on it the LED lights in the absence of signal and the led goes out when carrier keyed .
BC23D00F-5314-4160-93CF-EA553A451590.jpg
7A47B481-CF4E-4CF8-9282-FD5133C51F8D.jpg
409B8BF2-315F-491B-B0ED-7E3F1E460058.jpg
Reconstituted boy
John Ryan
Posts: 36
Joined: 31 Mar 2021, 03:56
Location: Rotorua New Zealand

Re: Micron RX S/C output

Post by John Ryan »

Great to see another set put to use. That Fet module looks interesting. Love that Mc Gregor Tx. My first set was a Mc Gregor valve Tx and a Terrytone receiver. Built from kits.
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