Re: splitting voltage

On 23 Aug 2006 16:23:56 -0700, "randomname"
<randomname12345@xxxxxxxxx> wrote:

OK everyone, thanks so much for your input. I've put in so many hours
to this project and just want to see it finished. You all are a great
help.



So as I understand, here's what needs to be modified from the
schematics (please let me know if anything is wrong):

- I'm going to keep the power supply at 4x AA batteries, since the 555s
require 4.5v.
- I will add .01uF caps on each 555 going from pin 5 to ground (I still
don't get what this does.. won't the capacitor just charge up and then
sit there charged?)

---
Yes.

Basically, what that input is used for is to vary the period (or
frequency) of the output by changing the voltage on that input. If
that input isn't going to be used its an arguably good idea to
decouple it so that noise won't cause jitter in the timer's output.
---

- The diode parallel to the motor will be an n4001, (is this the
correct diode?)

---
1N4001
---

- Change the resistor values on the 555 timer that controls the motor
to represent about 40% duty cycle at 100Hz [I'll experiment with this
to find correct values]. Read below to see why 40%.



And here are things I'm not sure about:

- Adding a 100uH inductor where? From + rail to the joint just above
the motor?

---
Shouldn't need it.
---

- Adding diodes to the 555 timers. From + rail to pin 1?

---
No, like this: (View in courier)

+6V
+------+ |
+6V>--+--[1N4001>]--+------|Vcc | [LED]
| |+ | | |K
| [1000µF] | OUT|----+
| | | |
GND>--|-------------+------|GND |
| +------+
|
|
+--------------------------------------+
| |
| +----+----+
| | |
| [1N4001] [MOTOR]
| | |
| +------+ +----+----+
+6V>--+--[1N4001>]--+------|Vcc | |
|+ | | C
[1000µF] | OUT|---[R]--B
| | | E
GND>----------------+------|GND | |
+------+ GND


The rationale for the diodes is to isolate the timers from the
voltage drop the motor might cause by having a little supply to keep
them going until the motor turns off.

Note that the 1000µF caps charge up through the diodes, and if the
motor current causes the battery voltage to drop the caps will
supply current into the timers for a while...





More about the 3v motor: When connected purely to 2 C batteries (as it
was designed to do), it pumps a small stream of water about a foot up.
However, this stream of water is too much for what I need it for... my
specs call for an even tinier stream of water. Ideally, I'd like to be
able to control how much water is flowing, which is why I'm opting for
the PWM solution, so I can effectively control the voltage, and as a
bonus get to use another potentiometer that controls something. Since
3v is too much, I'd like to try around 2 - 2.8 volts, just enough to
barely pump the water up. So I'm thinking roughly 40% duty cycle should
do it.

---
Probably more like 10%


--
John Fields
Professional Circuit Designer
.

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