Serial (without emulation side)?

[jazz 209]

I think that 3.3V is enough to power the MAX232 but the margin is very close. 3.0V (or less depending on charge) seems to be below the margin. Using a wall wart will supply a constant 3.3V through the regulator that seems to be enough to trigger the logic on the MAX232.

 

I think the FTDI entered the conversation as a way to allow you to program the chip without having the emulation side connected in order to save power if using a battery. The MAX3232 might be a valid option to allow the device to work on the battery running at or below 3.0V.

My point is... why using something (standard MAX232 chip) that maybe works OK with low voltage (close to 3V), when you can use something (MAX3232 or any other 3V rated chip with enough drv/rec) that is working OK for sure with low voltage (close to 3V by data sheet spec, and can go under). Don't see any reason for connecting MAX chip to any other supply voltage (to 5V why?), then MSP430 supply (battery, close to 3V).

 

As I understood, in this topic user want to use (battery powered standalone device) MSP430 with MAX chip for sending data to POS. There is problem in RS232 interface between MSP430 and POS, and there is no reason for putting FTDI chip in this story. Or maybe I don't understand the problem, don't know?

[jazz 209]

For example, this is my BSL, where (3V rated) MAX chip is used for RS232 communication, and it's powered by MSP430 power supply (regulated 3V or less, 3.3V or more, battery, whatever...). BTW, bit rate can go much over 115200 bps (with MSP430F5510 1.2 Mbps).

 

[cde 334]

Oh, duh meagan. Reread the thread. If it was working with the launchpad powered by usb, yet the max232 connected to the vcc, it worked because the max232 was getting ~3.5v. That's what the launchpad regulator provides. 2 AA batteries will give anywhere from 3.2v at best, 3v~2.7v at nominal, and 2v or lower by the time they discharge.

 

You could use 3 rechargeable nimh AAs, (1.4 at best, 1.2~1.1 nominal, steep drop at end, but last longer at the stated voltage). That will give 3.6~3.3 on average, and should work better.

 

TL;DR: 2 AA won't power a max232, but 3 Rechargeable (decent brand) AA should.

[mixographer 2]

Thanks for all the input on this. Yes, the MAX232 was working under the usb power, but I wanted to get the LaunchPad off my computer, so I (under)powered it with 2 1.5 alkalines. I didn't want to power it with 3x1.5 because I didn't understand where the VREG was connected. I'll try to get a low power 232 chip somewhere.

 

Thanks

 

Jimmy

[cde 334]

Thanks for all the input on this. Yes, the MAX232 was working under the usb power, but I wanted to get the LaunchPad off my computer, so I (under)powered it with 2 1.5 alkalines. I didn't want to power it with 3x1.5 because I didn't understand where the VREG was connected. I'll try to get a low power 232 chip somewhere.

 

Thanks

 

Jimmy

 

Another option, Take a spare mini-usb cable, cut it in half, and solder a 3x1.5 battery pack to red(v+) and black(v-). (Or solder the battery pack to tp3 (gnd) and tp1 (v+) by the usb connector. The tps77301 regulator will then power the rest of the board. It only needs 3.7~3.8v to work properly, anything above that (like 4.5v) is great.