cassette tape motor speed control

[KB3BYT]

I'd like to make a standard off the shelf five dollar cassette tape player slow down to half or quarter speed.
A tape player has a 1.7 volt two wire DC motor.
It seems that feeding it 1.2 volts will run slower but no more push..so it stalls.
I was wondering if I can pulse the full 1.7 volts real fast.....maybe at a few Hz.... so the motor has enough volts to push the drive belt but missing a beat here and there to make it move slower rpms.
We had a teriffic discussion on the old list about using pulses to slow down AC
motors with solid state relays to make the rollers go slower in laminators
we were doing heat applications of printed circuit boards and laser printer schematics.
I was wondering if that same logic could be applied to make a cassette tape motor run slower...but still have enough strength to push the tape.
The end use would be to tape morse code on the radio and then play it back slower for the new guys who don't understand fast morse code yet.
Any advice about what pulse rate I should target the circuitry around?
Rob KB3BYT

[keithdoxey]

Will the motor stand a HIGHER voltage ?

If so, make it run fast for the recording then playback at normal speed which will give the same result.

[Melanie]

Seems like a very archaic way of doing things...

Since a PIC can send perfect morse at whatever speed you want electronically, you can simply fill-up an EEPROM with ASCII data downloaded from a PC serially (or have the PIC generate random characters), set the speed you want and away it goes... and no moving parts other than a loudspeaker cone!

[KB3BYT]

This idea is that we have new radio operators that listen to the high speed morse on the radio and its just too fast for them so if we give them the opportunity to capture it and replay it ...maybe slower...then they get to have
a real world sense of whats going on instead of being locked into only listening to code practice.... computer generated or PIC generated.. or tapes.
So I figured that the basic $5 players available everywhere were perfect to
chop up and get at the motor speed control.
They don't have record heads....the $5 units only do playback..... so
I don't wnat to figure out how to ruin a tape recorder... they cost more...
I just want to make a player get the speed dropped for playback.
So back to the task at hand......
what frequency would be the right frequency to pulse a DC motor so that it
slowed the motor but didn't make it stall?
And is it OK to do that with a PIC12C509 or PIC16F84 or PIC16F628...etc..
with minimal part list. I'm thinking of making two buttons control pulse rate
UP and DOWN and one output pin running the 1.7 volt DC motor.
We would not even care if the pulsing made for a grainy playback.
It would still be slow morse code and the dits and dahs would be understandable.

[Melanie]

Those cheap motors have a working torque curve disproportionate to their supply voltage... best thing is to spend $5 and try it... but also consider...

1. You halve the playback speed, you halve the TONE... nice 400Hz Morse doesn't sound too good when played back say at 100Hz quarter speed.

2. Small DC motors running at below their optimal speed will run HOT.

Coincidentally, there I was going through a little Hamlet in deep green leafy England the other day and stopped to browse an Antiquariat that caught my eye (as if you didn't already know, girls live to shop)... There in a dusty corner was an original and boxed 12" vynil Record (you know the kind of thing people bought for entertainment before they invented CD's) - original 1960's "Teach Yourself Morse Code". As you got more proficient, you dialled up the speed on your record deck from 16rpm to 78rpm. Hands up anyone who's got a Record Deck with that speed range nowadays!

[KB3BYT]

Yes I agree that halving tone will make for some raspy CW but its not the tone
thats important in this project...its the ability to give the novices a shot at
nearly real time decoding what they hear go by at blistering speeds.
I may do this with a 555 instead of a PIC.
I will post all results of this experiment...good or bad.

My brand new TEAC retro console mimic has 33 44 and 78. I was playing 78s last week. They truly do suck.
I've been listening to http://www.shoutcast.com and digitising into mp3 for so long now that I forgot just how bad
radio and vinyl sounds. I carry a gumstick size 512 mb music toy that holds 100 tunes on it when I take a bus.
Oh ...and yes..... I am familiar with the various old code teaching methods with records and also paper tape.
I actually have an old paper tape contraption that plays CW with 3 inch reels of paper tape.
Its fun to sit that next to the PIC12C509 mint can code practice toy when showing off the hobby.
Its shows the range of technology from paper and tubes to SMD.

[Watlingfen]

In the 1967 British TV serial 'The Prisoner' this was the question that destroyed the then super modern computer..........
I can't quite understand why you can't simply buy a normal micro cassette recorder, record Morse at 2.4 , play at 1.2 , whilst this would be far less cost effective than your idea, a '1.7volt motor' supplied at 1.2v, even going to basic e=mc2 could not run and pulse feeding would come up with the same basic result = no run.
The idea of say supplying the '1.7v motor' with 4v might work - for a while before the smoke drifts up. I think you'll find your 1.7v motor is used to (and designed for) 1.5v average supply volts so can run at 1.2v or 1.7v with only very minor speed variation of the 4.75 cms per second - in theory for half speed to the tape you'd have to be able to run it at about 0.7volts ! - Not on old chap. Though I assume you have experimented with both series feed and parallel shunt resistors the one decreasing the current the other the load - this ploy was used in the 1940's to 60's by reel tape deck designers to reduce (considerably) volts to take-up motors on play only, switching out the high wattage resistor when 'rewind' in operation.
No, I have no experience of micro CD recorders, but the use of a micro cassette recorder then perhaps feeding a standard cassette recorder from earphone jack via paralleled capacitor (.01mf) and resistor (about 1kohm) per channel into line input of standard cassette recorder , making master tape then duplicating on a high speed dubbing double deck unit (which has the effect of slightly increasing the upper register of the sound) might be the answer to supplying a whole class with off-air recordings. I do so agree the lab-tutorial Morse tapes are hellish boring.
I do not agree with the observations on vinyl disc or even shellac 78 rpm record play quality (crackles not withstanding) - it does very much depend on the quality of pick-up, player, filters/amplifier and size/quality of woofers and tweeters speakers. Please remember this was analogue state of the art then - one day folks will look back on our discs (CDs DVDs etc) and smile as the EEPROM still has a lot of development before truly solid state record/playback of any time duration and frequency response can be achieved digitally. Best wishes.