Powering the SX28

DosManDan

My first post here, and I hate to ask such a basic question. I'm taking my design from the professional dev board to a standalone perf board. I will be using an LM2940CT to regulate the power. In the spec sheet for the LM2940, it recommends a minimum capacitor of 22uF, for stability. But, when I read an earlier article that showed the LM2940 in a circuit with a BS2, it only used a 10uF capacitor. Of course, I bought 10uF capacitors.... so, should I start wiring them in parallel to get up·past 22uF, or will it work with 10uF? Hate to mess up the SX over something so small.

Since I've finally had the courage to post, let me take a moment to say how impressed I've been with the products from Parallax. I've been buying products from them for the past 4 or 5 months, and have been able to successfully complete every project I've started. The availability of documentation and·wide variety of parts has been fantastic. I know the normal readers of this board already·are aware of the quality products from Parallax, so I guess this part of the post is directed at people who may be reading this that aren't yet customers.

Thank you for your time,
Dan

Forrest

I'd go with the latest datasheet recommendations. The SX requires quilte a lot of current when it's being programmed and one of the experts on this forum found that switching to a 22 uF capacitor solved intermittant programming problems. If you're using Servo's in your project - you'd be wise and install both the 22 uF and a 1000 uF capacitor - as the servo's can demand a lot of power.

Bean

Dan,
· Two problems can occur if the caps values are too small.
· One is a voltage drop (brown-out) when the circuit draw a larger amount of current
· The other is that the regulator may self-oscillate, this causes the regulator to draw alot of power and get hot.

Bean.

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DosManDan

Yes, I will be using a RLP434 receiver and servos in one of the SX circuits. This particular one is using a transmitter, 12 Key number pad and an LCD panel.

I appreciate the information, and I'll be sure to watch for those symptoms if something isn't working right. I'll wire up 3 of the 10uF capacitors, in parallel, until I can order the 22uF and 1000uF capacitors.

Thanks again, I appreciate the speedy responses,
Dan