Lpc2000

Hello Leon,

In first instance I used a HC244 and it was working fine in combination 
with the KEIL MCB2100 board. After several days I connected some extra 
hardware to the board and I was debugging the circuit with the 
oscilloscope. A 'led blink' program was running and I saw the 3.3V 
supply 'bouncing' between 3.3V and 3.6V. If the leds were 'on' then 
circuit was sinking more current than the LPT port could deliver and the 
result was 3.3V. If the leds were 'off' then the circuit was powered by 
the LPT-port instead of the 3.3V regulator. If I didn't measure the 
voltage in the circuit then I probably never discovered this because the 
software was running as expected.

BTW there is another power issue but this is related to the MCB2100 
board. On my MCB2100 board the 3.3V supply had a ripple. I read the 
datasheets from the LD1117S33 regulator, which is used on the MCB2100, 
and found that all the specs were based on a circuit whit a 10uF output 
capacitor on the regulator. As far as I know this capacitor is not 
present on the MCB2100 board. I soldered one at the bottom of the board 
and now the ripple is gone and the voltage is a stable 3.3V.

Have a nice weekend,
Aalt

-- 
==============================
Aalt Lokhorst
Schut Geometrische Meettechniek bv
Duinkerkenstraat 21
9723 BN Groningen
P.O. Box 5225
9700 GE Groningen
The Netherlands
Tel: +31-50-5877877
Fax: +31-50-5877899
E-mail: Lokhorst@...
==============================

Leon Heller wrote:
> ----- Original Message -----
> From: "Aalt Lokhorst" <lokhorst@...>
> To: <lpc2000@yahoogroups.com>
> Sent: Friday, April 08, 2005 11:26 AM
> Subject: Re: [lpc2000] Re: Wiggler with LPC2124
> 
> 
>  >
>  > Hello Leon,
>  > I am using your circuit without problems. I had only one issue.
>  >
>  > In your schematic is a HC244 buffer. The problem with this one, at least
>  > with the Philips type, it is not 5V tolerant. If it is powered by 3.3V
>  > then the inputs should not exceed 3.3V. It depends on the LPT port if
>  > this will happen. I think the LVC244 is a better choice just in case the
>  > LPT port delivers strong 5V levels. I have seen situations where the
>  > 3.3V of the circuit was lifted by the voltage from the LPT port.
>  > (Because of the diodes between the input and the VCC in the HC device)
> 
> I just checked the voltages on my port and they were about 4.8 V, but I
> haven't had any problems; I used the Philips part, but all HC parts should
> be the same. I'll amend the design, anyway.
> 
> 
>  >
>  > We are using the Rowley CrossWorks software.
>  > (Nice software and very fast responding support people)
> 
> I use their software as well.
> 
> Leon
> --
> Leon Heller, G1HSM
> http://www.geocities.com/leon_heller
> 
> 
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