No reset button? A fix!
Charlieb000
New
just letting everyone know that i have solved one of the greatest engineering disasters in the PC world - no reset button!
it annoys me not having one. i checked a "new" dell computer that was given to me and there is no reset button header, and after time on the net i saw that some have a button mounted on the board, but alas not there (and they made sure of it). i even did some research on how a reset button is connected and found that i need a strange 5 pin IC (TPS3823-33 or the like). it was almost easy to find the pads and pin 1 is still connected somehow, so i had this option if i wanted to do some smd soldering, and make a little web of components above the boad.
time went by and then i had a thought. why not use the Power Good signal?
i looked up wikipedia, ( http://en.wikipedia.org/wiki/Power_Good_Signal ) it seems to do what i want. after an interruption it causes the computer to read from the BIOS.
After designing some brilliant circuits, it didnt work! it turns out the board has a pull up resistor and i needed to drop that signal upon a reset, and also pass the PSU signal through, while accomodating for switch bounce!
i use falstad's circuit simulator, so heres the circuit code.
Version two (works!), acknowleding the MB pull up resistor:
four parts: PNP, 1k, diode, 0.1uF (104).
=========================================
$ 1 5.0E-6 10.20027730826997 50 5.0 43
d 320 272 320 160 1 0.805904783
w 320 272 208 272 0
w 320 160 208 160 0
w 320 272 384 272 0
w 416 272 480 272 0
w 400 224 400 160 0
r 320 160 400 160 0 1000.0
w 400 160 480 160 0
c 480 272 480 160 0 1.0E-7 -4.999999999949964
w 480 272 576 160 0
t 400 224 400 272 1 -1 4.999999999949964 4.9963588821810845E-11 100.0
s 480 160 576 160 0 1 false
g 480 272 480 320 0
r 208 272 208 160 0 2000.0
R 208 160 176 160 0 0 40.0 5.0 0.0 0.0 0.5
x 228 144 296 148 0 18 PSU PG
x 82 294 309 298 0 18 motherboard PG with pull up
if you cant read that, then:
the diode cathode (bar) is connected to PSU-PG, the diode anode to MB-PG (can now support components, if mounting on the PSU cable) and to the emitter. the resistor to PSU-PG, and the other end to the base.
the capacitor is across the base and collector, the reset switch across the capacitor. the collector is connected to GND.
according to simulator, i dont need another resistor on the base of the transistor.
if your motherboard has no pull up resistor to 5V you will need to add one, so one circuit fits all.
legal junk: free for everyone (11-2-12), information about normal reset switches from a EEE 900 (REV 1.25sec) schematic.
enjoy!
it annoys me not having one. i checked a "new" dell computer that was given to me and there is no reset button header, and after time on the net i saw that some have a button mounted on the board, but alas not there (and they made sure of it). i even did some research on how a reset button is connected and found that i need a strange 5 pin IC (TPS3823-33 or the like). it was almost easy to find the pads and pin 1 is still connected somehow, so i had this option if i wanted to do some smd soldering, and make a little web of components above the boad.
time went by and then i had a thought. why not use the Power Good signal?
i looked up wikipedia, ( http://en.wikipedia.org/wiki/Power_Good_Signal ) it seems to do what i want. after an interruption it causes the computer to read from the BIOS.
After designing some brilliant circuits, it didnt work! it turns out the board has a pull up resistor and i needed to drop that signal upon a reset, and also pass the PSU signal through, while accomodating for switch bounce!
i use falstad's circuit simulator, so heres the circuit code.
Version two (works!), acknowleding the MB pull up resistor:
four parts: PNP, 1k, diode, 0.1uF (104).
=========================================
$ 1 5.0E-6 10.20027730826997 50 5.0 43
d 320 272 320 160 1 0.805904783
w 320 272 208 272 0
w 320 160 208 160 0
w 320 272 384 272 0
w 416 272 480 272 0
w 400 224 400 160 0
r 320 160 400 160 0 1000.0
w 400 160 480 160 0
c 480 272 480 160 0 1.0E-7 -4.999999999949964
w 480 272 576 160 0
t 400 224 400 272 1 -1 4.999999999949964 4.9963588821810845E-11 100.0
s 480 160 576 160 0 1 false
g 480 272 480 320 0
r 208 272 208 160 0 2000.0
R 208 160 176 160 0 0 40.0 5.0 0.0 0.0 0.5
x 228 144 296 148 0 18 PSU PG
x 82 294 309 298 0 18 motherboard PG with pull up
if you cant read that, then:
the diode cathode (bar) is connected to PSU-PG, the diode anode to MB-PG (can now support components, if mounting on the PSU cable) and to the emitter. the resistor to PSU-PG, and the other end to the base.
the capacitor is across the base and collector, the reset switch across the capacitor. the collector is connected to GND.
according to simulator, i dont need another resistor on the base of the transistor.
if your motherboard has no pull up resistor to 5V you will need to add one, so one circuit fits all.
legal junk: free for everyone (11-2-12), information about normal reset switches from a EEE 900 (REV 1.25sec) schematic.
enjoy!
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