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Calamar
Joined: 07 Sep 2003 Posts: 60 Location: Buenos Aires (Argentina)
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Driver holtek HT1620 |
Posted: Thu Mar 08, 2007 8:36 am |
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Some one worked with ht162x??
My circuit board is like the showed in
HT1620 datasheet, page 11 rev 1.20
but the Vlcd is not enought with the
the 3Meg resistor, using a 680K
resistor (instead 3Meg) the Vlcd
reach almost 4.0V is it the way
to increase de Vlcd voltage ? _________________ Best Regards
Daniel H. Sagarra
La Plata (Argentina) |
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Humberto
Joined: 08 Sep 2003 Posts: 1215 Location: Buenos Aires, La Reina del Plata
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Posted: Thu Mar 08, 2007 10:08 am |
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Hola Calamar.
I never used this display, but regarding your question I found the following
info in the Holtek documentation:
http://www.holtek.com.tw/english/tech/faq/RAMlcd_faq.htm
"The problem of uneven illumination of LCD pixels can be caused
by insufficient drive current from the LCD driver, this can be resolved in 2 ways:
By using LCD panels with a COM-SEG capacitance value of less than 10pf, reducing
the size of the pixels and choosing higher quality displays are all measures
which can be used to increase impedance and reduce the loading effects of the
application circuit.
Increase the current drive of the HT1650/1660/1670
Increase VLCD, which will increase the Vrms-on and Vrms-off window, which will
increase the light/dark contrast.
Choose a large Bias Current.
Choosing a suitable resistor value (about 1K) to be placed between the pins
VDD -T1, T1-T2, T2-T3, T3-T4, T4-T000 and T000-VSS etc and choosing a suitable
capacitance value (about 0.1uF) to be placed between the pins T1-VSS andT4-VSS
will reduce the output impedance and increase the drive current capability of the device. "
Hope this help you,
saludos
Humberto |
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Calamar
Joined: 07 Sep 2003 Posts: 60 Location: Buenos Aires (Argentina)
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Posted: Thu Mar 08, 2007 11:05 am |
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Thank you Humberto, but the info don't match with the
HT1620. There is any way to paste the
circuit in the post ? I would like post the schematic,
may be some one with experience over lcd drivers
and charge pump could give me a cloud... _________________ Best Regards
Daniel H. Sagarra
La Plata (Argentina) |
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Humberto
Joined: 08 Sep 2003 Posts: 1215 Location: Buenos Aires, La Reina del Plata
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Posted: Thu Mar 08, 2007 2:41 pm |
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Quote: |
using a 680K resistor (instead 3Meg) the Vlcd reach almost 4.0V
is it the way to increase de Vlcd voltage ?
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This voltage should depend of the value of the capacitor connected in CC1/CC2 actually 0,1uF
I don't know why are you trying to change this value, but if your problem is a poor
LCD contrast, this is not the first time I know of this problem with this family of IC.
The HT1620 is an old IC. It have been replaced by the HT1621 wich doesn't have
at all the conflictive Pin VO15N (Half Voltage circuit Output Pin) you are fighting with.
The HT1621 has the advantage that it include two pins to connect a potentiometer
to adjust the LCD contrast.
You are aware that Holtek is very conservative (poor) at the time you need relevant
technical info of your products. Normally they give you the minimum info required to
start working and you will expect nothing more.
Another characteristic in its sales policy is that they could stop manufacturing
any IC without a reasonable previous advice, or would replace it for an "upgraded"
version, without releasing the corresponding technical information of the change,
so you will never know.
Saludos,
Humberto |
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Calamar
Joined: 07 Sep 2003 Posts: 60 Location: Buenos Aires (Argentina)
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Posted: Thu Mar 08, 2007 3:21 pm |
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yes my problem is poor LCD contrast, I change
the r=3Megohm value because the data sheet
dont specify what to do,, where did say that instead
it I should change the value capacitor conected in
CC1/CC2 ?
My glass LCD work with 4.Xv and the MCU is a
MSP430 power a litium cell so I choice the HT1620
because it has a charge pump.
Where are your from (city) ?
Saludos Daniel _________________ Best Regards
Daniel H. Sagarra
La Plata (Argentina) |
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Humberto
Joined: 08 Sep 2003 Posts: 1215 Location: Buenos Aires, La Reina del Plata
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Posted: Thu Mar 08, 2007 3:32 pm |
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Holtek HT1620 Datasheet (I have more than 4 versions, the last is from July, 1999)
Page 2:
Notes: CS: Chip selection
BZ, BZ: Tone outputs
WR, RD, DATA: Serial interface
COM0~COM3, SEG0~SEG31: LCD outputs
IRQ: Time base or WDT overflow output
VO15N: Half voltage circuit output pin
VEE: Double voltage circuit output pin
CC1/CC2: External capacitor pin, for double voltage and half voltage circuit use
If you want to contact me pls. use the private msg option.
Saludos,
Humberto |
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