arduinobreadboardcircuit analysiscircuit-design
I've made an arduino circuit for my high school physics project. It uses an ultrasonic and an infrared detector to sense distances and operate a Servo and Leds and I am having troubles with the circuit diagram.
Can someone explain to me how I can represent an ultrasonic sensor, an infrared sensor and a servo in a circuit diagram? The ultrasonic sensor has 4 pins. Echo, trigger, ground and Voltage. The infrared and Servo have 3 each. The block diagram is as below
In this answer I showed that the optimal series resistor value is
\$ R_S = \sqrt{R_{MIN} \cdot R_{MAX}} \$
where \$R_{MIN}\$ and \$R_{MAX}\$ are the minimum and maximum resistances of your sensor. The Sparkfun page speaks of between infinity and 300 kΩ. If we assume 10 MΩ as maximum value then your series resistor should be 1.8 MΩ (rounded to nearest E12 value).
These are pretty high values, too high for an ADC, which, like Mathieu says, likes a impedance of less than 10 kΩ. So you'll need to buffer the divider with an unity gain buffer opamp:
Note that a common opamp may have an input bias current as high as 1 µA, and this could distort your reading. A CMOS opamp like the MCP600x has a much lower input bias current, 1 pA typical for the MCP600x, which won't deteriorate your reading.
According to the document you provided, the datasette port is looking for a pure digital signal with varying duty cycle (0.75 for H, 0.25 for L).
As long as the Arduino pin can drive sufficient current (it should be able to) and is operating at 5V, a direct connection will work. You may want to investigate using a TTL buffer between the Arduino and the C64 (the buffer would be powered from the +5 supply of the datasette port, and the ground would be common to both the C64 and Arduino).
As for the SENSE, it would be easier to use a digital output to drive a small-signal MOSFET (like a 2N7002) - a logic high turns the MOSFET on, which pulls the SENSE pin (connected to the drain) to ground (connected to the source) without the Arduino having to sink any current at all.
The MOTOR pin could also be used to drive a MOSFET gate. The drain would be pulled up to the Arduino supply voltage with a weak pullup (10k or so), the source connected to ground. The drain would also go to a digital logic pin. When MOTOR is high, the logic input is low, and vice versa, and the Arduino sees a clean logic signal.
For example...
Note using two NAND gates as a buffer of sorts. (Can you tell I used to scrounge for parts?)
TTL is fairly robust. I don't think there's much chance of damaging anything.
Best Answer
We use rectangular boxes with all the signals as labelled pins for components which have no specific schematic diagram symbol.
There is a simple schematic editor available if you edit your question. Press CTRL+M and it'll pop up. It includes common symbols for resistors, LEDs, batteries, etc.
To make it easier to read a diagram there are conventions. Negative or ground is a horizontal line along the bottom of the diagram, below components, and the voltage rail is a horizontal line along the top, above the components. These conventions help us to understand the diagram more quickly. They also help to show current flow, through parts of the circuit, as lines from top to bottom. So there is less 'clutter', and the whole diagram becomes easer to read.
For example, here is an incomplete diagram based on your photograph:
simulate this circuit – Schematic created using CircuitLab