The Museum of HP Calculators
HP Forum Archive 13
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Message #1 Posted by Eric Lundgren on 5 Oct 2003, 5:10 p.m.
Well, I buckled down and got the 48gx, it appears to be the black screen, but have any of you noticed a 'pulsing' of the screen. Its barely noticeable until you turn the contrast really dark. Just curious, this thing's gotta get me through my BSME! ...saving the 32sii in a dry cool box for the eventual PE fiasco.
Any new-user tips from you all?
|Re: HP48GX newcomer|
Message #2 Posted by r. d. bärtschiger. on 5 Oct 2003, 5:43 p.m.,
in response to message #1 by Eric Lundgren
I think the pulsing depends on the type of ambiant lighting. Yes, mine has it also when the contrast is turned up.
|Re: HP48GX newcomer|
Message #3 Posted by Ed Look on 5 Oct 2003, 6:08 p.m.,
in response to message #2 by r. d. bärtschiger.
Someone correctly pointed out on this forum that the refresh rate on 48G screens are a bit over 64 Hz so that if a light has frequency of 60 or so Hz, then the interference "pulsing" is seen.
Message #4 Posted by Tom (UK) on 6 Oct 2003, 1:19 p.m.,
in response to message #3 by Ed Look
Normal bulbs pulse at 2x the ac frequency i.e. 100Hz or 120Hz, I'm not sure about strip lights.
The human eye can only 'see' pulsing up to about 25Hz as the eye has a low pass filter effect above that frequency. Strobe effects can easily bee seen if they are less than 25Hz.
Message #5 Posted by Ed Look on 6 Oct 2003, 1:29 p.m.,
in response to message #4 by Tom (UK)
Tom, in the US, power comes at 60 Hz. Some of our streetlamps seem to have that same frequency. I was using my HP48G under one once and I could see the flicker! I'm told that its screen refreshes at around 64 Hz or so. I think that information might even be found in this museum site somewhere...
Message #6 Posted by Tom (UK) on 7 Oct 2003, 12:44 p.m.,
in response to message #5 by Ed Look
I don't know what rate the HP48G series updates the screen. Does a 'normal' house bulb give the same result as a street light (i.e. pulsing display)? If it doesn't visibly pulse then there is possibly some other effect.
From my recollection of electronics; if a light bulb runs from 60Hz the light will pulse at 120Hz. In the UK the mains electricity is 50Hz so lights pulse at 100Hz.
Light intensity = Power = ((Voltage)^2) / Resistance
If Voltage = V x COS(freq)
Power cx= (V x COS(freq))^2
Power cx= V^2 x 1/2(1 + COS(2 x freq))
(where cx= is 'proportional to')
Message #7 Posted by Wayne Brown on 7 Oct 2003, 1:20 p.m.,
in response to message #6 by Tom (UK)
My office is lit by a combination of fluorescent lighting on the ceiling and daylight coming through large windows. I normally don't notice any flickering on my 48GX. Sometimes, usually late in the day when there is little daylight left and the fluorescent lights are providing most of the illumination, I notice a slight flicker. However, I have a small fluorescent light on my desk and when I examine the 48 under that light the flickering clearly is visible, especially if I view the screen at a shallow angle.
At home, where I have only incandescent lighting, I never see any flickering.
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