Hold circuit

[Dr. Ernst Baumgartner]

Hi,

my problem ist the following:

With a foot contact I switch a tiny power mosfet (BS 170) on, which in turn
(softly) turns on a small 9V DC motor. After a moment, my foot often gets
tired, and I would like some circuit to hold the gate of the mosfet positive
for me.

After a minute or two, I would like to be able to turn off my mosfet again
by a short touch to the pedal.

I was thinking of a combination of 555 timer(s) opening a time window where
I could take the foot off the pedal, and a sample an hold ic, but do not see
how to combine them, I am just an amateur...

Is there a genius out there who can help me to accomplish this?

Any input will be greatly appreciated, thank you in advance!

Ernesto

 

[Jasen Betts]

Hi,

my problem ist the following:

With a foot contact I switch a tiny power mosfet (BS 170) on, which in turn
(softly) turns on a small 9V DC motor. After a moment, my foot often gets
tired, and I would like some circuit to hold the gate of the mosfet positive
for me.

After a minute or two, I would like to be able to turn off my mosfet again
by a short touch to the pedal.

I was thinking of a combination of 555 timer(s) opening a time window where
I could take the foot off the pedal, and a sample an hold ic, but do not see
how to combine them, I am just an amateur...

Is there a genius out there who can help me to accomplish this?

Any input will be greatly appreciated, thank you in advance!

assuming your switch has dual-throw contacts

.-------------------------------------------------------------.
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`-------------------------------------------------------------'

+9V
+---------------+--+--------.
| X| | |
| .-----+ | |
| | | | |
===== | [47K]| . . . .|. . . .
|10u | | | . VCC(8) .
| |1u | | . . out
+-----+ ===== | `--RES(4) OUT(3)----+-----
| | | | . 555 . |
| .-|--o-_ +-----+-----TH(6) DIS(7)-- |
| | | -o--+ | . . |
| [1K]`--o `-----TR(2) CV(5)-- |
| | . . |
| \ . GND(1) . |
| \| . . . .|. . . . |
| |--[10K]-------------------|----------'
| |/| |
[220K] /~ NPN (eg BC547/2n3904) |
| | |
`---+-----------------------------+
0V

 

[pintlar]

Would a 'push on / push off' switch work?
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