Power Questions

flying_flip

Hi,
I'm really new to the forum, and relatively new to basic stamping.

Question 1:
I have a 2 components that I would like to get to work together.
1 - Parallax 2x16 Serial LCD (backlit)
1 - Parallax GPS

Running on BS2 although I just bought a BS2PX

When I run the components separately, they work fine.
When I attempt to run both, the LCD backlight, turns off.

I am thinking that it is just the Power supplied to the board. (6v 130ma)
As the LCD with backlit is 80ma draw and the GPS is 115ma, the board basically turns off the backlight to save current draw.
If it's current draw then 20ma+115ma is still above the amperage supplied by the power supply.


Question 2:
The program I am designing is to be used on a scooter.
MPH, Time, Direction, and #sats will all be displayed on the LCD.
I might even put in Turn signal annuciator.

I am hoping to put this all on a circuit board to save my BOE for prototyping.
What do I need to supply 5-6v, and 1 amp max, from my scooter battery, when it fluctuates for 11 to 14 volts, and is a 7amp/h battery.
I don't want to fry the Stamp.

Thanks in advance.

sylvie369

It runs okay with the backlight off, though? That'd confirm that it's a power problem.

flyingflip said...
The program I am designing is to be used on a scooter.
MPH, Time, Direction, and #sats will all be displayed on the LCD.
I might even put in Turn signal annuciator.

On a 2x16 LCD? You're going to be cycling through them one or two at a time, then, right? I've built the device you're working on (using a 4xAA battery holder with a BS2pe Mobo, and it worked fine, though with no backlight), using the 4x16 LCD, and even with that I'd have liked more LCD real estate.

flyingflip said...
am hoping to put this all on a circuit board to save my BOE for prototyping.
What do I need to supply 5-6v, and 1 amp max, from my scooter battery, when it fluctuates for 11 to 14 volts, and is a 7amp/h battery.

You're going to build a circuit around the 2px module, then? The modules have built-in voltage regulators.

Parallax website guy said...

<A name="Power the Stamp">How do I power the BASIC Stamp module?</A>

The BS1 and BS2 modules both require 5 volts DC (Vdd) or 5.5 to 15 volts DC (Vin). The BS2e, BS2sx, BS2p24, BS2p40, BS2pe and BS2px24 all require 5 volts DC (Vdd) or 5.5 to 12 volts DC (Vin). All Stamps feature an on-board 5-volt regulator which will convert an input of 5.5 to 12 volts (5.5 to 15 volts for the BS1 and BS2) on the Vin pin down to the 5 volts that it’s components require. If your power supply is 5.5 to 12 volts (15 volts for the BS1 and BS2), you should connect it directly to the Vin and GND pins or to the battery clips on the development board. The Vin and GND pins are pin number 1 and 12 on the BASIC Stamp Rev. Dx module, pin number 1 and 2 on the BS1-IC or pin number 24 and 23 on the BS2-IC, BS2E-IC, BS2SX-IC, BS2P24-IC, BS2PE-IC and BS2PX24-IC (40 and 39 on the BS2P40-IC). If your power supply delivers a regulated 5 volts, you should connect it directly to the +5V (Vdd) and GND pins (2 and 12 on the BASIC Stamp Rev. Dx, 5 and 2 on the BS1-IC, and 21 and 23 on the BS2-IC, BS2E-IC, BS2SX-IC, BS2P24-IC, BS2PE-IC and BS2PX24-IC (37 and 39 on the BS2P40-IC). NOTE: When using battery or wall-pack power supplies, it is recommended to limit the voltage to 9 volts on the Stamp 1 and Stamp 2, and 7.5 volts on the Stamp 2e, Stamp 2sx, Stamp 2p, Stamp 2pe and Stamp 2px.

You might be able to regulate your 11-14Vdc supply to 7.5Vdc, send that to Vin, and then power the GPS and LCD from the Vdd pin on the module. However, I'm guessing: wait for someone who knows what he's talking about (like the guy below me <grin>) to chip in, okay? I'm just putting up some relevant information here.

Post Edited (sylvie369) : 11/29/2008 9:11:46 PM GMT

SRLM

You could probably use a voltage regulator (like the square block in the heat sink on the BOE) You don't want to use the Basic Stamp built in voltage regulators to power the LCD and GPS: I don't recall off the top of my head how much it can provide, but it certainly can't handle all that.

flying_flip

The 2 components do work together.
If I try to use the backlight, the "system" turns it off.
(lcd initailized first)
The display still functions as programmed.


All the code still fits on the BS2 so, I would like to keep it on that.
Yes, I would cycle the MPH more often then the other items. Time display
is in Hours minutes, so doesn't need the refresh that often.

The MPH display is kinda nice in that I'm using the 8 custom characters ( 0-9 definitions in eeprom)
to display the digits in 2x2 format (easier to read on a vibrating scotter), on the left,
The time in the upper right hh:mm
Directional Text ( N,NE,E...) and S:## to display sats in the bottom right.
Lots of rooom.

So a Voltage regulator is all I need to curb the Battery voltage down?
No capacitors or other components?


Thanks,

Phil

sylvie369

flying_flip said...


So a Voltage regulator is all I need to curb the Battery voltage down?
No capacitors or other components?

Ooh, I'm betting you'll need capacitors, and a diode, so you wind up with something similar to this:



www.tkk.fi/Misc/Electronics/circuits/psu_5v.html



I'd hold tight here for a day or two and see who else pipes up here. There are a lot of people on this forum who can tell you exactly how to do it - I'm sure you'll get a good definitive response.

Carl Hayes

You don't need a bypass capacitor at the input of the regulator if your input power is reasonably clean (such as from a battery rather than from a transformer & rectifier). If you were drawing constant (or nearly constant) current you wouldn't need a capacitor on the output either.

However, if the current you draw varies quickly (as it certainly will when you're feeding digital devices), you ought to place a capacitor at the output, because the capacitor can react with (theoretically) infinite speed, while the regulator is limited by the very modest slew rate of the amplifier inside it.

Best practice is to use, at the regulator output, a moderately large electrolytic capacitor (say 50 μF) in parallel with a non-electrolytic of perhaps 0.01 to 0.1 μF. Many electrolytic capacitors have significant series inductance (because they're made by winding metal foil around a spool) and cannot react as quickly as other types, so we use an electrolytic to handle the big changes while the regulator catches up, and a small non-electrolytic to handle the small but fast changes while the regulator catches up. The effect is to decouple the loads from each other, so that changes in the current drawn by THIS load don't cause a transient change in the voltage supplied to THAT load.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net

flying_flip

Thanks Sylvie and Carl.

I think I have the ammo I need.

Phil