I'm trying to use the MSP430, specifically the ez430-rf2500 to power some
solid state relays.

What happens when the outport port bit on the MSP430 is set to high?

Is it tied directly to +3.3V (Vs) or is there a series current limiting
resistor there? What is the value of this resistor?

Same question when the output port bit is set to low:

Is it tied directly to GND or is there a series current limiting resistor
there? What is the value of this resistor?

This information would help me figure out what the voltage drop across the
relay inputs are to determine what value of resistor I need to put in there.

Thanks in advance.
Henry
[Non-text portions of this message have been removed]
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Because you use a SSR and not knowing it's part number, I will assume ( Al will cringe here:) that your relay Has a TTL/CMOS type input. For those parts I use automatically a 4.7K resistor series and a 10Kohm to ground to control the input pin. If you can be sure that the processor control pin will never be in HIZ then the 10K is not necessary.

Yf you have a low power design, you can try a 47/100Kohm resistor combination. This will save some miliampers.
Without Wax,
BB

--- On Sat, 8/2/08, Henry Liu wrote:

> From: Henry Liu
> Subject: [msp430] Basic MSP430 question
> To: m...@yahoogroups.com
> Date: Saturday, August 2, 2008, 6:12 PM
> I'm trying to use the MSP430, specifically the
> ez430-rf2500 to power some
> solid state relays.
>
> What happens when the outport port bit on the MSP430 is set
> to high?
>
> Is it tied directly to +3.3V (Vs) or is there a series
> current limiting
> resistor there? What is the value of this resistor?
>
> Same question when the output port bit is set to low:
>
> Is it tied directly to GND or is there a series current
> limiting resistor
> there? What is the value of this resistor?
>
> This information would help me figure out what the voltage
> drop across the
> relay inputs are to determine what value of resistor I need
> to put in there.
>
> Thanks in advance.
> Henry
> [Non-text portions of this message have been removed]
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Being a solid state device, the equivalent resistor you asked about
varies from chip to chip and also depends on temperature, operating
voltage, and current. You can find typical voltage vs. current curves
at 25C/85C and operating voltage at 2.2V/3V in Figure 4, 5, 6, and 7
in the data-sheet SLAS504B.pdf.

Roughly speaking, the equivalent resistor is something like 40 ohms
when the current is limited to 25 mA.

--- In m...@yahoogroups.com, "Henry Liu" wrote:
>
> I'm trying to use the MSP430, specifically the ez430-rf2500 to power
some
> solid state relays.
>
> What happens when the outport port bit on the MSP430 is set to high?
>
> Is it tied directly to +3.3V (Vs) or is there a series current limiting
> resistor there? What is the value of this resistor?
>
> Same question when the output port bit is set to low:
>
> Is it tied directly to GND or is there a series current limiting
resistor
> there? What is the value of this resistor?
>
> This information would help me figure out what the voltage drop
across the
> relay inputs are to determine what value of resistor I need to put
in there.
>
> Thanks in advance.
> Henry
> [Non-text portions of this message have been removed]
>

------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

"old_cow_yellow" :

> Roughly speaking, the equivalent resistor is something like 40 ohms
> when the current is limited to 25 mA.

Well, according to the datasheet - you should not draw more than 2mA from/to
each pin.

M.

------------------------------------



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