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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 1st Aug 2021, 12:37 pm   #1
tritone
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Default Motor control & Lamp/LDR circuit boards

Hello Forum,

Would anyone like to explain a little more on these please?

I found a several of these simple little project circuit boards in the junk pile, I think that they were for a secondary school electronic student project.

The first one is a type of speed/timed motor control.

The second board is for an LDR controlled lamp circuit.

I have several of these, I can give some away if there is any interest.

The first and second pic's are the motor control board, the third and fourth pic’s are the lamp/LDR boards.

Cheers.
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Old 1st Aug 2021, 2:47 pm   #2
TonyDuell
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Default Re: Motor control & Lamp/LDR circuit boards

They seem to show the PCB traces looking on the track side of the board.

The motor controller is a pulse-width modulator thing. A 555 connected as an astable (oscillator) with variable resistors to set the on and off times (notice the diode in parellel with the resistor between pins 6 and 7 of the 555, so esentially the timing capactor charges through the resistor between the +ve rail and pin 7, then via the diode to the capacitor and discharges through the resistor between 6 and 7, the diode then being reverse-biased into pin 7 to ground). The output of the 555 drives a TIP121 power darlington transistor which controls the motor.

The second board would seem to be a thing to turn a lamp (6V bulb) on when it gets dark. The base of the TIP121 is connected to a potential divider consisting of a variable resistor and the LDR. So as it gets dark, the LDR resistance increases, the base voltage rises and when it gets to about 1.4V (Darlington, remember so 2 diode drops between base and emitter) current flows into the base and thus current can flow through the load. The variable resistor lets you set the light level for this to occur. It will not turn on/off sharply, it probably works fine in the lab when you cover the LDR with you hand, less well if uses to sense nightfall.
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Old 1st Aug 2021, 5:43 pm   #3
MotorBikeLes
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Default Re: Motor control & Lamp/LDR circuit boards

Presumably, if the LDR was on the board, it would be a low frequency oscillator?
Les.
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Old 1st Aug 2021, 9:34 pm   #4
Sound Man
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Default Re: Motor control & Lamp/LDR circuit boards

Just a thought, could it be that the LDR circuit is for an electronic candle. The LDR is pointed towards the lamp. When a lighted match is held next to the lamp it is switched on and because the LDR is near the lamp the circuit will keep the lamp lite. Cover the lamp with a finger to distinguish it.

David
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Old 2nd Aug 2021, 4:46 am   #5
TonyDuell
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Default Re: Motor control & Lamp/LDR circuit boards

No, it's the wrong way round for that. You'd have to interchange the LDR and the resistors in the potential divider circuit.

Going back to a previous post, to get an oscillator don't you need a sharp turn on/off preferably with hysteresis?
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Old 2nd Aug 2021, 7:57 am   #6
tritone
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Default Re: Motor control & Lamp/LDR circuit boards

Hello Tony, Wow,,, thats fantastic, great info, Thank you so much Sir & everyone !


Also, I found these LDR's in a box, I have about 30 of them.

Im going to construct/build/complete a few of these boards, I'll let you's know soon. They will be F.O.C. when ready,

Many thank you's to you Tony, Soundman, & MotorBikeLes,
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Old 2nd Aug 2021, 3:51 pm   #7
G6ONEDave
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Default Re: Motor control & Lamp/LDR circuit boards

I thought that the LDR circuit was simply a night light type of circuit that illuminates the bulb once the LDR decides that it's getting dark, the darkness level being adjusted by the pre-set.

Dave
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Old 3rd Aug 2021, 12:05 pm   #8
wave solder
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Default Re: Motor control & Lamp/LDR circuit boards

The ORP12 LDR, I remember all of the experiments I did with it when I was a school. ��
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