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Three reaction time games This circuit provides three games to measure the fastest reaction time of the players. Which game is played is chosen by the GAME SELECT switch (S2), and instructions are shown on the LCD screen. Game one gives one player four chances to get the best reaction time. Game two is designed for two players, each having two chances. Game three can be played by two, three or four players, each with only one chance. By default, the device is set to game one for one player. To play the game, apply power and wait for the “Press Start Button” message on the LCD screen. The game begins by pressing the START/RESET button (S7), causing LED1 to start blinking randomly 1 to 3 times. Then it stays lit, and the sounder beeps to signal to the player to press the PLAYER 1 button (S3). At this point, an increasing counter appears on the lefthand side of the first line of the LCD. It counts up in milliseconds from 1 to 8000. At the appropriate time (when LED1 stays lit or the beep is heard), the player must press PLAYER 1 (S3) as fast as they can to stop the counter. This causes a second counter to appear on the left side of the second line, and it starts counting up. Right away, the player must press PLAYER 2 (S4) to stop this counter 90 Silicon Chip and start a third counter on the third line, then press PLAYER 3 (S5) to stop this counter and start another on the fourth line. Finally, the player presses PLAYER 4 (S6) to stop that counter. The four counters now show the registered reaction times, with the sum of the reaction times of the four steps on the right-hand side of the bottom line. The lower the value, the shorter or faster the reaction time of the player’s finger. Game two is selected by a long press of pushbutton S2. The first player uses the S3 and S4 buttons, while the second player to S5 and S6 buttons. Again, the game begins by pressing the S7 button, causing LED1 to flash randomly one to three times and then stay lit while the sounder generates a beep. At this moment, two counters appear on the left and right sides of the top line. Right away, players one and two must press S3 and S5 respectively to stop these counters and cause two more to appear on the second line, and these start counting up. Then they must press S4 and S6 to stop counters these counters. The reaction times of both players are now registered, and their sums are shown on the third line of the LCD. The player with the lower value of the sum (faster reaction time) is the winner. The winner is also displayed on Australia's electronics magazine the fourth line (for instance, “Winner: Player 2”). Game three is selected by another long press of S2. To select the number of players (2-4), press and hold S4, S5 or S6 for a two, three or four-player game respectively, then press S7 and release both. For instance, to select a two-player game, press and hold S4 first and then S7 and finally release both buttons. In a four-player game, there are four counters on the left side of the four lines of the LCD, which all start siliconchip.com.au NBN backup battery at 0. The game begins by pressing S7, causing LED1 to flash randomly one to three times and then remain on while the sounder generates a beep. Once LED1 is on, or the beep is generated, all four counters start counting up in milliseconds from 1 to 8000. Now each player should press their own pushbutton switches as fast as possible to stop their relevant counters. The fastest player to press their button wins. Then the player with the quickest finger or the minimum reaction time (the minimum counter value) is announced as the winner on the LCD screen (eg, “Winner: Player 4”). It’s possible to have multiple winners if the buttons are pressed simultaneously. In all three games, if a button is pressed too early (in the start status while LED1 is blinking), it will continue flashing, and the sounder will beep until the button is released. Then after another random flashing cycle, LED1 will stay on while a beep is made to signal to the players to press the play buttons to resume the game. If one or more buttons are not pressed within eight seconds (8000 milliseconds), the counters stop at 8001. The display will then clear to show “Timeout Error” on the first line and “Press start button to play again” on the third and fourth lines. To reset and restart the game, press S7. The software for this circuit can be downloaded from: siliconchip.com. au/Shop/6/6339 Mahmood Alimohammadi, Tehran, Iran. ($80) siliconchip.com.au Having recently had the NBN installed, I found that now I had two devices (the NBN modem and the wireless router) both powered by plugpacks and both dependent on mains power to keep working. We get the occasional blackout in my area, and without these devices, I have no internet connection on my tablets and other battery-powered devices. Reading past articles in Silicon Chip inspired me to design a simple backup power supply. The circuit operates as follows. The mains power supply is connected via CON1. I used one of the NBN plugpacks (12V DC). IC1 is a precision adjustable shunt regulator, but is being used here as an open-collector comparator with a precision voltage reference connected to one of its inputs. With voltage across CON1, transistor Q1 is switched on and it pulls the reference input of IC1 low. This prevents IC1’s output transistor from conducting, so Q2 is off, and the only path to output connector CON3 is from CON1 via schottky diode D1. LED1 is also lit as it is powered from the DC supply, indicating normal operation. When the plugpack voltage disappears, as long as the battery voltage is above 9.25V, IC1’s reference input is allowed to rise above 2.5V. So IC1 sinks current from its anode terminal, switching transistor Q2 on, supplying the output from the backup battery. Australia's electronics magazine Since I used a lithium-ion battery as the backup battery, I needed to be able to disconnect the output if the backup battery voltage fell below 9V. You would probably change the 27kW resistor to 33kW for a lead-acid battery, raising the cut-out threshold to 10.75V. The green LED indicates that plugpack power is available, and the red LED indicates when the output is supplied from the battery. If both LEDs are off, there is no output voltage. This circuit does not include any way for the battery to be charged, because where I live, power outages are infrequent and I am happy to recharge or swap the battery manually every few months. If you need to keep the battery charged, you can permanently connect a mains trickle charger (for lead-acid types) or lithium-ion maintenance charger to the battery. D1 should be a schottky diode of sufficient rating for the load current. Transistor Q2 can be any PNP transistor rated for the output current; something in a TO-126 or TO-220 package will do, and it does not have to be heatsinked. I built my version on stripboard and housed it in a small plastic box. Of course, this can be adapted for many other uses where a simple backup supply is required. Robert Budniak, Denistone, NSW. ($80) April 2022  91