delay off timer circuit

Hi, I have a project that I am stuck on and would be really happy if I
got a solution.
I have two machines that both have footswitch controls with 1/4" jacks.
The main unit turns on when the pedal is pressed and off when it's
released. The second unit turns on when the pedal is pressed and off
when it's pressed a second time. What I want is an adjustable splitter
that accepts one footswitch and has leads that plug into both units. I
want both units to turn on together and when the pedal is released I
want the main unit to stop and the second unit to stop after a time
delay (variable from 1-10 seconds). Also, if the pedal is pressed again
before the second unit has stopped, I want both units to be on and the
second unit's off-delay restarted when the pedal is released.
I've played with some 555 timer circuits and relays, but can't figure
this out. The voltage on the pedals is low (<24).
I need help!
Anyone know a circuit that could be a solution to my problems?????

 

I've played with some 555 timer circuits and relays, but can't figure

I'd probably use a small CPU, probably a PIC. You may need
some extra just for level shifting.

 

The pedals are just switches. Either pedal works in both units the
same. I want them both to turn on when the pedal's pressed. When the
pedal's released I want the main unit to go off and the second unit
starts a delay for the off.

 

+---------------+--[RY2]---+---------+
| | | |
| +----|<----+ |
| D3 | |d (c)
| FS |<
+12 ---+---o o---+----+--->|---+---+----g| |s (e)
| | | | D2 | | |
|> | | | +| \R1 |
[RY1] [D1] [C1] /<-+ |
| |a | \ | |
| | | | | |
Gnd --------------+----+--------+---+--+----+

+--------+---o--- Ry1-1
| | ^---------[Machine1]---+
Machine | |
Power +---o--- Ry2-1 |
Source ^---------[Machine2]---+
| |
+--------------------------------------+


When you step on the foot switch (FS), relay RY1
is energized directly, and relay RY2 is energized
via the power mosfet, which is turned on by +12
at its gate. The +12 volts also charges C1 almost
instantly. When the footswitch is released, RY1
drops out immediately, but RY2 remains energized
by the charge on C1. C1 discharges slowly through
potentiometer R1, which adjusts how long it takes.
When C1 discharges sufficiently, the mosfet turns
off and RY2 drops. The normally open contacts of
RY1 and RY2 are wired in series with the power source
for the machines and machine 1 and machine2 respectively.

Use a cheap N channel power mosfet, a 22 uf cap
and a 1 meg pot. Alternatively, use an NPN
power darlington like a TIP 120 (note the emitter
and collector designations). Select 12 volt relays
with contacts rated to switch the machines.

Ed

 

_________ _________ ____________
FS ____| |____________| |__| |_________
_________ _________ ____________
M1C____| |____________| |__| |_________
_________ _________ ____________
M1on___| |____________| |__| |_________
__ __ __ __
M2C____| |___________| |____| |___________________________| |__
____ ____ ____
Delay____________| |_________________| |__________| |_____
______________ ______________________________
M2on___| |_______| |_____

To make things clear I sketched the diagram above. (View with fixed font).
So we see the status of FootSwitch, Machine_1_Control, Machine_1_on/off,
Machine_2_Control, machine_2_switchoff_Delay and Machine_2_on/off. It will
be obvious that Machine_1 simply follows the footswitch and that you will
need two timers. One to make the Machine_2_Control pulse the other to make
the Delay.

From the diagram you can read that you have to trigger Delay on the trailing
(falling) edge of FS. You have to trigger the M2C timer on the leading
(rising) edge of FS *unless* Delay is high *and* on the trailing edge of
Delay *unless* FS is high. As you have timers already, I give an idea of the
logic. The circuit below should work for you.

||
FS----+-----------||-----+----+----+
| || | | |
| .-. | |
| | | - |
| | | ^ |
| '-' | |
| | | | __
| ----+----+ +---| | __
| |\ |& |-----|>=|
Delay---)---| >O---+---------------------|__| |1 |----M2C_trigger
| |/ | +--|__|
| | |
| | || __ |
| +--||---+---+---------| | |
| || | | |& |--+
| .-. | ----|__|
| | | | |
| | | - |
| '-' ^ |
| | | |
| ------+---+ |
| |\ |
+---| >O---------------------+
|/
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

You can use NAND gates and use the fourth gate as an extra inverter. 555
timers require negative trigger pulses.

petrus bitbyter