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Ronnie Ericsson

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In Reply to: Optical detectors posted by Jacques on August 25, 2006 at 01:55:22:

I thing the fork type looks good for the application.
No need to attach a reflective surface, and no risk of engaging the lift by mistake!
Just takes a little "screen" thing to stick out from the arm (or perhaps use the whole arm tube for the screen).
I'm no good with transistors. What supply voltage range does the transistor in this one like (see link)?

HONEYWELL OPTO PRODUCTS HOA1877-002 (Open in New Window)

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Re: Sweet! - Jacques 01:35:50 08/28/06 (3)
30V is the absolute max value. 24V is the practical max value.
With 24V:
Use a 33kohm resistor as collector load, you'll get about 0,6mA collector curent when on, which is fine.
As for the LED, use a 2,2KOhm resistor in serie with the anode. You'll get 10mA LED current, which is fine.
I would advise you to use some timer (a simple 555 would make the job fine) in order to get a pulse with a predetermined duration, which would be used to lift the tonearm.
In this case, have the voltage at about 12V. Decrease resistors in accordance.
- Re: Sweet! - Ronnie Ericsson 13:14:58 08/30/06 (2)
  Does that mean the transistor switches abruptly between 0mA (OFF) and 0.6mA (ON)?
  I was thinking of driving some kind of motorized ball-screw actuator (directly off the transistor if possible). Perhaps some kind of minimotor..
  - Re: Sweet! - Jacques 09:41:19 09/06/06 (1)
    Does that mean the transistor switches abruptly between 0mA (OFF) and 0.6mA (ON)?
    
    Yes. Have a collector load resistor with a value so that, when the phototransistor is ON, a current <0.6mA flows. For example, if your power supply is 12V, to get such a current, you get a resistor 12V/0.6mA = 20KOhms without any margin. So, use a 33Kohm, 5% and you're done.
    
    was thinking of driving some kind of motorized ball-screw actuator (directly off the transistor if possible)
    . Not possible: you won't get more than 0.6mA from the phototransistor, which is way too small to move an actuator.
    
    You should use a timer like the 555, directly triggered by the phototransistor. The micromotor can be fed directly from the 555 (100mA output capable). Furthermore, by adjusting the timer delay, the micromotor would run the requested time, and not stop once he has moved the tonearm away from the light detector.
    Google out application note about the 555, it is well known by tinkerers., and cost about $0.1.
    
    Perhaps some kind of minimotor..
    
    As for micromotors, you should cannibalize a dead cheap camera. The lens motor is well fit to your need.
    - Aha! Thanks a lot! (nt) - Ronnie Ericsson 04:54:09 09/09/06 (0)

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