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Sir Ezekiel . . . . .
Preamble . . . .
Sometimes back you were trying to figure out a Belkin AC wall timer of yours.
I had started my reply for you, with the creation of a 1:1 front / back PCB illustration.
Then, after my "reading" and fully analyzing its on board circuitry, I was seeing a very simple solution.
Somehow , I did not finish the accompanying text portion and post it for you.
In my minds eye, though, I thought both had already been done long ago.
I just now ran across its illustration on a flash drive, and that jogged my memory, to check
back and see what had transpired.
Nothing . . . . since it had not been posted.
Its continuance . . . . .
Instead of all of the basic received suggestions of you having to reconstruct from scratch, the design of a wheel, then the laborious building of a wheel and a final debugging of a wheel,
lets just closely analyze to see what in actuality, you ALREADY have.
Your specified need is for a 3 interval timer of selective options of 2, 5 or 10 hours timing periods.
With the units present 30min, 3 hours and 6 hour options, this just looks to be equivalent of an Amerikanski to Metric / decimal " conversion" . . . but with it involving time periods instead.
Our first timing option just relates its 30 min to your needed 2 hours, or a one fourth slow down of the timing period.
The next timing is being a 3 hour to 5 hour relationship, NOT maintaining the same ratio, but its all important, same condition of the slowing of the timing period.
Lastly is the 6 hour to a needed 10 hour period, also being just like the situations before.
All timing periods need to be stre e e e e e e e tched out from their present values.
Now lets make a part by part run through of this boards design concept .
You have the male connectors for the AC input via the male ABC connectors and two of the connectors are passing directly thru the board to become 1 and 2 with the exception of the HOT line connector C.
That connection swings aside togo to E in order to connect in power relay D terminal and make a complete circuit when the relay 9 is activated.
Next consderation would be the minimal power required by the system with a high of 24 volts @ 20 ma needed by the relays coil.
In exploring the units power supply portion, we see line AC power coming into Start / Power switch 4 and then passing thru surge / dropping resistor #5 and then over to the TF1 fuse within the black cambric sleeve, with there being yet another foil link fuse F2 on the other side of the board. .
Looks like they had opted not to incorporate the MOV marked on the board and then AC went into the C1 poly cap. There is being about 1.2 meg of "bleeder' resistance shunted across that capacitor.
The combination of the initial R2's minor series resistance and the AC inductive reactance of the C1(#6) cap drops the voltage down to a proper reduced level that is then being applied to the discrete full wave bridge rectifier that is utilizing D-4-5-6-7 diodes.
The power supply area is contained within the yellow boxed area, with the FWB's just rectified DC then being routed over to the C3 (#10) storage /filter capacitor.
Regulation to a 24 volt level is established with the Z1 24V zener with a supplemental C5 ceramic capacitor used for zener shot noise and hi freq digital "trash" filtering.
Looks like R10 is supplying power to D2 GREEN LED from this supply.
This higher supply voltage is principally routed over to supply the (#9) relay coil. A minor power supply voltage is being branched off from this supply and routed over to the C4(#12)capacitor and its lower 5V zener diode and its shunting C6 ceramic capacitor.
That gets the units power supply covered, now for our main point of interest, which will be the U1 mini flat pack IC, the S1 timer period selector switch , and a timing capacitor and a series of resistors.
In order to be accomplishing the electronic timing and control tasks of this unit , by looking at U1 and functionally analyzing, it will have to be containing an oscillator circuit, which then feeds to a digital counter / divider chain and a final timer reset function along with a digital HIGH take off level for the base drive of Q1 relay driver transistor.
Of the final parts that I am seeing on the board , C2 appears to be serving as the C componenet of an RC oscillator pair,with R4 being its companion R unit, BUT with a special quirk, by the variation of stre e e e e e e tching the value of R by the insertion of 2 more series values of R, thru the S1 timer period selector switch.
The start of the units timer circuit has a HIGH digital output from the U1 IC which exits at the gold via that I have marked with the RED dot and travels on the other side of the board thru the RED dot path until it reaches the R8/R9 resistor voltage divider pair for a level shift then finally ends up at the RED dot gold via of the Q1 relay driver at its base.
The nearby D1, is used for relay coils back EMF spike suppression / protection .
Referring to the photo . . . foil side:
Note " backwards " 4R ( of ??? ohmmic value) and the fact that its LEFT terminal goes up to a test point, but also goes down to a gold via and dissapears.
That fine path on the opposite side of the board is hidden but pops up again as a gold via on the GREEN -BLUE junctions foil tab of the selector switch.
I have assigned GREEN-BLUE-TABS as the positions of the one shorting contact that would be traveling with the white control lever / knob in its 3 positions.
Looks like GREEN position would just be using the R4 and C2 time constants for generating the shortest 30 min period.
Move the timing knob down one click to the center and it inserts R1 resistor in series with R4 and the timing period has been slowed down to create the 3 hour period.
Finally, in the last position, yet another resistor is inserted in series to give the very longest timing period of 6 hours.
Your time now:
Take ohmmeter in hand on an UN powered unit and confirm my suspicions on the switches "shorting" actions as well as being my eyes on reading and passing back all of the resistors values.
The only ones I could make out were the 514 ones, of which I had to invert one and flip another to get their proper printing perspective you are now seeing, also, the R10 limiting resistorfor the GREEN LED was also being readable as 220.
Looks like the last resistor of the timing series string might just be the cramped up R11.
Play with your ohmmeter and the switches positions to confirm for us that the resistors are R4 and then R4 + R1 and finally R4 + R1 + R11
The first testing . . . . . in fully utilizing my Mac Guyver techniques . . . . .would be to set up in the 30 min mode and Plug in an old school AC powered motorized electric clock that runs if AC power is present or stops if you loose power and the hands freeze until power up again, to resume timekeeping.
You will set the clock to straight up 12:00 and plug into the timer and power up to initiate the timing cycle and thereby be able to make an aside observation of its accuracy, as it will be displayed for you right there with the hands stopped reading.
NOW you look at the R4 value and find a wire leaded resistor of approx 10 times that resistance value and solder tack it across R4 and run another timing cycle and note the timer variance will create a slightly "faster" time cycle.
If that test confirms creating a timing variance, we then know that we are dealing with the select timing components in that shortest timing cycle, THEN, a proper selected resistor of a HIGHER resistive value should cause that first timing period to shift to your needed 2 hours.
Use the same procedure of the changing of the values of the other two resistors to shift timing to 5 and 10 hours.
FIO . . . . those VIOLET circles are just designating that those foil areas are just bolstering support for the S1's mounting tabs, looking to be having no circuit connectivity.
CONDENSATION . . . . . select and change three resistors and you have it.
Pending your feedback and info.
MARKED UP 1:1 BOARD VIEWS . . . . .
73's de Edd
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