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Old 20th Dec 2018, 6:56 pm   #1
DonaldStott
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Default Turntable Stroboscope

Split from this thread: https://www.vintage-radio.net/forum/...d.php?t=152165

All this talk of oscillators and crystals reminded me that I've still to design and build a 300Hz strobe to help with adjusting my turntable(s) speed of rotation.

I know it's slightly off-topic but thought that something might have cropped in the Chinese AM radio kits arena - or if anyone would like to assist??
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Old 21st Dec 2018, 12:39 am   #2
SiriusHardware
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Default Re: More Chinese AM radio kits

300Hz strobe: Start with a common 2.457600MHz baud rate crystal, and divide it with a ripple counter down to 300Hz.

The easiest way to do that would be to use a single CMOS 4060 IC as both crystal oscillator and counter. The 300Hz output would be from pin 2 (divide by 8192), I think. Use that output to drive a LED on and off via a transistor.
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Old 21st Dec 2018, 6:11 am   #3
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Default Re: More Chinese AM radio kits

Some time ago I made a 100/120 flashes/second strobe. Started from a 4.9...MHz crystal oscillator module, then 3 common 74HCT chips. Drives 4 white LEDs. I built it for setting the spindle speed on old floppy disk drives (which had a strobe disk on the spindle pulley) and it was easily good enough for that and gives one of the clearest stationary patterns I have ever seen.

Of course the 2 flash rates let me use strobe disks either intended for 50Hz or 60Hz lighting.

I can provide the circuit diagram if anyone wants it.
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Old 21st Dec 2018, 10:55 am   #4
DonaldStott
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Default Re: More Chinese AM radio kits

Thanks Sirius and Tony

My circuit design skills are woefully lacking so any assistance whatsoever in this department would be extremely helpful. Always keen to learn, even at my age!
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Old 21st Dec 2018, 4:31 pm   #5
merlinmaxwell
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Default Re: Turntable Stroboscope

I got one of these https://www.ebay.co.uk/itm/1Hz-65534...YAAOSwQ5pb9pO3 for a work test jig, works well. A LED would work direct from the output.
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Old 21st Dec 2018, 4:42 pm   #6
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Default Re: Turntable Stroboscope

I've attached a scan of my circuit (sorry, I don't use CAD, I use a 'paper aided design' system, better known as a pad).

A couple of things : I've not shown the power and ground connections to the ICs, they go to +5V (output of the 7805) and ground. Also add a 100nF disk ceramic capacitor between +5V and ground close to each IC (that is probably overkill when it comes to decoupling but such capacitors are a lot cheaper than my debugging time, at least for a one-off).

The thing runs off a 12v wall-wart type power supply.

There is a 2-pole 3-way switch. Centre position is off. Flipped one way you get 100 flashes/second. The other way you get 120.

The LEDs are on for 1/16th of the time. A short flash (rather than 50:50 on/off ratio) gives a clearer 'still' pattern of the strobe disk.

You are welcome to make this non-commerically. If you start selling them then I feel I deserve something in return.
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Old 21st Dec 2018, 4:53 pm   #7
ian_rodger
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Default Re: Turntable Stroboscope

Sounds like a good Arduino project. An attiny85 (8 pin chip) and an LED might be all you need assuming it can run an output at 300 Hz with the Arduino code overhead. Should be a simple programme. If I have time this weekend I'll test that for you and report back.
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Old 21st Dec 2018, 5:54 pm   #8
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Default Re: Turntable Stroboscope

Yes that works with attiny 85. I tested it using the attiny's built in oscillator but you would probably want to use an external xtal for stability. There is also the possbility to programme a few selectable frequencies if tou want. If you are not familiar with programming Arduino's (lots of good tutorials on youtube) then I would be happy to program the chip for you. Programme (sketch) below. Assumes an led is connected to pin 7 via a suitable resistor.

/*
Strobe at 300Hz

LED connect from pin 7 to ground via suitable current limit resistor
*/
int LED = 1; // PB1 maps to pin 6 on attiny85
// the setup function runs once when you press reset or power the board
void setup() {
// initialize digital pin LED_BUILTIN as an output.
pinMode(LED, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
digitalWrite(LED, HIGH); // turn the LED on (HIGH is the voltage level)
delayMicroseconds (333); // delay 333 uS
digitalWrite(LED, LOW); // turn the LED off by making the voltage LOW
delayMicroseconds (3000); // delay 3000 uS

}
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Old 21st Dec 2018, 7:20 pm   #9
SiriusHardware
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Default Re: Turntable Stroboscope

Ian's method is the way to go if you happen to have an Arduino on hand as the hardware is built for you, even down to there being an LED already on the PCB.

If you prefer a basic electronic circuit, this 4060 oscillator / divider (attached, from the internet), might be a good starting point. The output you'd need to use for 300Hz would be from pin 2, and you'd have to use that to drive a transistor or darlington pair, in turn driving an LED.
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Old 22nd Dec 2018, 12:09 pm   #10
DonaldStott
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Default Re: Turntable Stroboscope

Wow - thanks guys but unfortunately a bit beyond my knowledge and understanding"

What I really need now is to find a Ladybird "Guide to Oscillators and Crystals", a Look and Learn "Oscillator/Dividers/Counters" supplement but appreciate I've no chance of sourcing an Eagle Annual cutaway drawing explaining "How a CMOS 4060 IC works"!

These days it's all "Idiots Guides .. " !

Looks like more R&D is needed on my part so I'll get onto this Project in the New Year.

Meantime best wishes to everyone for the Festive Period and for a prosperous New Year.
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Old 24th Dec 2018, 11:10 am   #11
Herald1360
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Default Re: Turntable Stroboscope

The circuit shows the crystal oscillator bits (the active bits are inside the chip).

The 4060 itself is simply an oscillator and a string of 14 binary dividers with most of the intermediate divider stage outputs brought out to pins. It's very useful for producing long, reasonably accurate time delays without resorting to gigohm and farad RC circuits
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Old 2nd Jan 2019, 7:53 pm   #12
DonaldStott
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Default Re: Turntable Stroboscope

Happy New Year to all on the Forum.

Getting back on track with my planned 300 Hz strobe I managed to borrow a "commercial" product from a friend and took pictures of the board and components - many unmarked!

It's based on a 4.9152 crystal and an HEF4060BP binary counter/divider and oscillator.

What's the easiest way to reverse engineer a circuit diagram from a picture of a board - I'd like to understand what is going on rather than just lash up a DIY copy.

I'll probably need some help in identifying the value and type of certain components further down the line but meantime can anyone identify the diodes in the attached pictures - I can't see any markings?
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Old 2nd Jan 2019, 8:06 pm   #13
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Default Re: Turntable Stroboscope

Probably silicon general purpose diodes, 1N914 or 1N4148

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Old 17th Jan 2019, 2:40 pm   #14
DonaldStott
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Default Re: Turntable Stroboscope

Looking for a bit more technical assistance as I try to educate myself on how Oscillators and Crystals work in a circuit.

As mentioned above I'm trying to construct a 300 Hz strobe based around a 4.9152 crystal and an HEF4060BP binary counter/divider and oscillator. Looking at the Product data sheet for the HEF4060BP we have the Pin out diagram : -

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I'm confused by how you calculate the counter out values when there is no Q1, Q2 or Q10 - see here for the Pin description table: -

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To get from 4915200 Hz to 300 Hz I need to divide by 2 ^14 i.e. 16384 - so, put simply, what pin would that be??

I appreciate I need to build a circuit involving caps and resistors to get the whole thing oscillating and that a Darlington pair will be required to drive an LED - I'll also need some judiciously place diodes.

Small steps ...
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Old 17th Jan 2019, 3:51 pm   #15
merlinmaxwell
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Default Re: Turntable Stroboscope

Use Q13, it starts at Q0 so that is 14 in real money. Funnily enough I recommended this chip to a work colleague a few days ago for a time out function, my brain sucked it out of the dim and distant past.
Quote:
I appreciate I need to build a circuit involving caps and resistors to get the whole thing oscillating and that a Darlington pair will be required to drive an LED
The datasheet gives the circuit for crystal use, a couple of caps and a resistor. If you run it from 5V (three 1.5V cells is good) it will drive a white LED directly, no resistor or transistor needed. Modern LEDs are very bright and the chip won't mind.
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Old 17th Jan 2019, 4:26 pm   #16
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by DonaldStott View Post
I'm confused by how you calculate the counter out values when there is no Q1, Q2 or Q10 - see here for the Pin description
This data sheet should clear the confusion:

https://pdf1.alldatasheet.com/datash...HEF4060BP.html

Lawrence.
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Old 17th Jan 2019, 4:28 pm   #17
DonaldStott
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by merlinmaxwell View Post
Use Q13, it starts at Q0 so that is 14 in real money.
Thanks - makes perfect sense now that I know it starts at Q0 - so that's pin 3 on the HEF4060BP!

Quote:
The datasheet gives the circuit for crystal use, a couple of caps and a resistor. If you run it from 5V (three 1.5V cells is good) it will drive a white LED directly, no resistor or transistor needed. Modern LEDs are very bright and the chip won't mind.
The circuit I was working on runs from a 9V battery and includes a Darlington pair, several resistors and capacitors, including electrolytics, along with some diodes to prevent back voltage. Something based on this: -

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Your solution sounds much simpler to the extent that I may build both just out of curiosity and my own further education.
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Old 17th Jan 2019, 8:48 pm   #18
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Default Re: Turntable Stroboscope

It will be unusual for any stock crystal to be unaffected by the circuit loading, so you can
replace one of the 22pF caps with a 66pF trimmer, and that will enable fine frequency
adjustment, when measured with a frequency meter. It also allows junk box crystals
to be pulled to the desired output.
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Old 17th Jan 2019, 9:51 pm   #19
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Default Re: Turntable Stroboscope

Your output circuit is far too complicated. Use a 1k resistor to the base, (no capacitor), use a simple transistor with emitter connected to ground, put the LED in series with the collector resistor. If you need a lot of current use a n channel FET, there is plenty of voltage to drive it.
No diodes are needed but a capacitor across the chip power supply would be good.

White LEDs use fluorescence, I do not know whether they have a long time constant
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Old 18th Jan 2019, 12:41 pm   #20
DonaldStott
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by Restoration73 View Post
... you can replace one of the 22pF caps with a 66pF trimmer...
Would this one be appropriate - seems a bit expensive: -

https://www.cricklewoodelectronics.com/CTR80908003.html

The circuit in the Product data sheet for the HEF4060BP shows a bias Resistor with the values 100 kΩ to 1 MΩ - should this be a variable Resistor?

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