Conrad Course material 10107 14 years and over 10107 Manual De Usuario
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10107
The value of the permissible current through the LED depends on the type used and must be checked in the manufacturer's datasheet if
in doubt. The light-emitting diodes used in this learning package are standard components that will light up even at a current of 1–2 mA.
The forward voltage is 2.0 V at a yellow LED, 2.1 V at a red and 2.4 V at a green one. The LED should be operated with a current of
approx. 2 mA. This information can be used to calculate the dropping resistor for the LED.
in doubt. The light-emitting diodes used in this learning package are standard components that will light up even at a current of 1–2 mA.
The forward voltage is 2.0 V at a yellow LED, 2.1 V at a red and 2.4 V at a green one. The LED should be operated with a current of
approx. 2 mA. This information can be used to calculate the dropping resistor for the LED.
R
V
R
V
U
Batt
– U
LED
U
Batt
– U
LED
I
LED
I
LED
9 V – 2,1 V
9 V to 2.1 V
2 mA
2 mA
3450 Ω
3450
Ω
Since there is no resistor with 3450
Ω in the resistor standard series, you will need to use the closest value.
In this case, this is a resistor of 3.3 k
Ω.
3.2 Hot Wire with Memory
This example is an expansion of the preceding one. The rules of the game are the same. If the light-emitting diode only lights up while
the wire is touched, the players will argue quickly. One saw the LED light up and the other claims it didn't. To remove this problem, the
circuit is expanded by a memory mechanism. Now the light-emitting diode will no longer go out after the wire has been touched. The
LED can only be switched off again with the button.
R1
R1
R2
R2
R3
R3
R4
R4
V1
V1
V2
V2
Fig. 13: Hot Wire with memory
The circuit has been additionally expanded by a green light-emitting diode that shows that the circuit works and that no contact has
taken place yet. If the red LED is lit instead of the green one after connecting the supply voltage, push the button briefly to reset the
circuit to the starting condition.
taken place yet. If the red LED is lit instead of the green one after connecting the supply voltage, push the button briefly to reset the
circuit to the starting condition.
Circuit Description
The two NAND-gates (IC1A and IC1B) are used to implement a NAND-flip-flop. The NAND-flip-flop works like an RS-flip-flop with inverted
inputs. Therefore, the condition of the output can be changed with a low level at the input. The resistors R1 and R2 are pull-up-resistors
and apply a high level to the inputs. If the wire is touched with the loop, a ground potential is applied to the pin 1 of IC1A and thus
corresponding to a low level. To understand the flip-flop circuit, you need to assume a stable condition. Assuming that the green LED is
lit and pin 4 therefore has a high level, then pin 2 has a high level as well. If pin 1 is pulled to low level by a contact, pin 3 will switch to
high according to the NAND function. This level is applied to pin 5 as well. While the button is not pushed, both inputs of IC1B are on a
high level and the output is set to low. This leads to the green LED (V2) going out and the red one (V1) lighting up. If the button is pushed
and the wire is not touched, the green LED goes on according to the same functional principle while the red goes out. If the wire is
touched while the button is pushed, the condition is undefined. This should be avoided since there is no clear result.
inputs. Therefore, the condition of the output can be changed with a low level at the input. The resistors R1 and R2 are pull-up-resistors
and apply a high level to the inputs. If the wire is touched with the loop, a ground potential is applied to the pin 1 of IC1A and thus
corresponding to a low level. To understand the flip-flop circuit, you need to assume a stable condition. Assuming that the green LED is
lit and pin 4 therefore has a high level, then pin 2 has a high level as well. If pin 1 is pulled to low level by a contact, pin 3 will switch to
high according to the NAND function. This level is applied to pin 5 as well. While the button is not pushed, both inputs of IC1B are on a
high level and the output is set to low. This leads to the green LED (V2) going out and the red one (V1) lighting up. If the button is pushed
and the wire is not touched, the green LED goes on according to the same functional principle while the red goes out. If the wire is
touched while the button is pushed, the condition is undefined. This should be avoided since there is no clear result.