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All of Nutchip inputs can be connected to TTL or CMOS outputs - the latter only when power supply voltage is the same as Nutchips, 5V.
The example on the right shows how to connect a logic AND gate output to a Nutchip input.

Should you need to connect Nutchip inputs to a DC voltage higher than 5V, you must reduce it to safer levels, for example using a couple of resistors as shown here.

12V signals are often found in alarm systems, as the voltage is required to power electronic sensors. A signal voltage swing of 12V is also advantageous to increase noise immunity: as signal voltage will by reduced by about 2/3 by the resistor divider, the same will happen to noise spikes captured by input wiring. Such noise-rejection effect can be improved even further connecting a 100nF capacitor in parallel to R2.

• When using this circuit for 24 volts input increase R1 to 2200 ohm.

When galavanic separation between external circuitry and Nutchips circuit is required, an optocoupler can be used easily. Optocouplers are specialized ICs were an LED faces a phototransistor. Externa circuit clamps to M1. When the external circuit is off, or as long as the voltage across M1 is less than 1 volt, the phototransistor is not off and Nutchip input will read as 1.

Voltages around 5V will lit the LED, bringing the phototransistor to conduction. As the transistor is across the input and GND, the Nutchip will then read zero.

• measuring a resistor
• implement a knob-control to set variable delays

Here is how it works:

• keep the output at logic level zero, long enough to fully discharge capacitor C1. Usually this requires at least twice the maximum time to be set with potentiometer POT1.
• Set the output to one. Starting now, the input reads zero until capacitor C1 charges to at least 2V.
  

Note: we recommend to add a 220 ohm resistor in series with the output to protect the Nutchip in case the potentiometer be set to zero-resistance.

This is an improved version with respect to previous circuit, allowing a fast capacitor discharge thanks to diode D1.

This addition allows to reduce the time when the output is kept to zero in order to discharge the capacitor; otherwise the circuit works in the same way of the previous one.

Note: we recommend to add also a 220 ohm resistor in series with the output to reduce peak current.

A mechanical "quadrature" encoder is equivalent to a couple of switches. These parts usually require just three pins because of a COMmon pin joining two internal switches.

Using a multimeter, discover which pin is in common by turning the knob while measuring pin-to-pin resistance.

Some encoders have both switches closed while standing in rest position, others either A or B, lastly some others have both switches closed.

Magnet activated switch, also named reed switches, are often used for detecting door and windows opening in an alarm system. Reed switches are small hermetic switches whose contact opens or closes under the effect of a strong magnet nearby. The most popular open the contact when away from the magnet. As long as the magnet is in close proximity (e.g. windows closed) the contact is closed, therefore should a burglar cut alarm wires the alarm will trigger as well.

Reed switches connections are the same as common switches or pushbuttons. When connected across Nutchip input and positive power supply, 5V, a pull-down resistor R1 (around 470 ohm, but any value from 100 ohm to 1000 ohm will do) is necessary to contrast the internal pull-up action of Nutchip's integrated resistors. As reed switches are often placed remotely, a make-to-12V or alarm circuit could be a better chioce. See also the alarm system design for practical circuit example.

The simplest way to connect a reed (magnetic) switch or a pushbutton to Nutchip inputs is across the input itself and GND. Nutchip inputs have an high-value internal resistor keeping them positive if not externally connected elsewere. Therefore, reding the input when the button is released gives a logic 1. Pressing the button connects it to GND, giving a logic 0 level.

When using a reed in an alarm system, see also the following circuit which improves rejection to noise captured by long connection wires.

Alarm sensors require (usually):

• 12 Vdc power supply. Power is supplied from the base.
• A normally-closed switch, it opens when the sensor detects an alarm source
• (optionally) an anti-tamper normally closed switch, it opens when the sensor lid is removed

Sometimes Nutchip is requested to detect AC signals coming from external devices:

• to detect a ringing bell (common ringers are of the 12 or 24 Vac types)
• to connect to an existing control panel in an electriic machine
• to detect limit switches, floaters, power relays, etc.

This is the preferred way to drive an LED froms logic output. It is a old times inheritance, when logic gates were capable to sink much more current when at logic level 0 - compared to current sourced when at logic level 1.

With this connection the LED lits when the output is at logic level zero (the LED current flows from +5V to Nutchip pin, following the arrow symbolizing the LED). When the output is set to logic level 1, the LED goes off (and no current is required from output pin.

The 390 ohm R! resistor limits current through the system. The suggested values limits the current around 10mA, as suggested by most LED manufacturers.

This schematic shows how to connect two LED to a single pin, with an interesting alterante effect - when an LED is on, the other is OFF and vice-versa. It is excellent for driving dual-color displays - e.g. a green LED as DL1 and a red one as DL2, in order to build a light that changes colour when the output flips.
Special LEDs encapsulating a common cathode+anode pair are commercially aailable, and can be used with this circuit in place of two separate LEDs.

When the output is high, LED DL2 is on and LED DL1 if off.
When the output is low, LED DL1 is on and LED DL2 is off.

Both resistor are 390 ohm. Overall current through the output pin will always be around 10mA, not 20mA as it could seem at a glance, because there is only one LED on at any given time.

Note: an intriguing behaviour of this circuit is that if you try building it, but omitting the connection to Nutchip's output pin, you will see both LED on. Can you tell why?

In order to build light effects, Christmas decorations, and flashing words, it is sometimes required to drive a large number of LEDs together.

This circuit can drive up to 12 LEDs for each Nutchip output (you can also use only 6 leds omitting the rightmost parts). If a LED-series needs less than 6 LEDs, increase the value of the relevant series resistor (R2 or R3) according to the following table.

As typical Nutchip output devices, relays are second only to LEDs. Thanks to a relay, a Nutchip output can drive lamps, motors, electric valves, transformers, heaters, pumps and many other devices.
Relays are manufactured in a variety of coil voltages. As long as the coils is a 5Vdc type, it can be powered by the same power as the Nutchip, whereas 9 or 12Vdc types require a dual-voltage power supply. It is usually not necessary to use a power regulator IC to stabilize a 12V relay power line, tough.

Relays are advantageous because the load (connected to clamp M1) is galvanically insulated from the Nutchip circuit.

DANGER: when using a relay for switching mains-powered loads, like a desk lamp, great care is required to ensure there are not unwanted connection between the live mains-powered parts (lamp, M1, relay contacts) and the rest of the circuit. Accidental contacts can kill you or cause severe damages, fires, and fry your PC. Do not try to connect anything to the mains without your teacher and an experienced electrician assistance. Ask your power company and electrician for regulations that may apply in your contry.

It is very handy to have an LED which lits when a realy is on. Resistor R2 varies from 390 ohm to 1000 ohm, according to coil voltage:

Small relays used in electronics circuits are not suitable for driving loads requiring more than a few amps - equivalent to roughly 200W at 220Vac. To drive heavier load an additional power relay is required. The smaller relay (RELAY1) drives the bigger one (RELAY2), which is a special type suitable for heavy loads (ask your electrician). The current on RELAY1 contacts is low - just enough to drive RELAY2 coil), but RELAY1 output contacts must be rated for at least 250Vac, because RELAY2 coil is mains-operated.

DANGER: great care is required to ensure there are not unwanted connection between the live mains-powered parts. Accidental contacts can kill you or cause severe damages, fires, and fry your PC. Do not try to connect anything to the mains without your teacher and an experienced electrician assistance.Ask your power company and electrician for regulations that may apply in your contry.

Any Nutchip output can drive a 5V buzzer, provided it is of the "all electronic" kind. Avoid using electro-mechanical types, ase they require far too much current that a Nutchip output can source, and can generate voltage spikes capable to damage the Nutchip output stages.

Tip: most 9V all-electronic buzzers work also at 5V, although at a reduced sound intensity.

12V buzzers are quite common and are also easily found as surplus parts. Sometimes they are so loud that "mini-siren" would be a more appropriate name. This circuit is suitable for buzzers requiring up to 100 mA. Should your siren require more current, use a relay to drive it.

DC lamps from 3 to 24Vdc can be driven with just one darlington-type transistor. Don't be fooled by the schematic, the symbol for a darlington is the same as a transistor pair! The voltage required by the lamps (+V) must be less than 40 volts, and the transistor type is TIP122.

Tip: switching the output on/off creates the illusion of modulating lamp luminosity

Light effects take advantage from using TRIACs instead of relays. Relays are unsuitable for continuous flashing operation, as their contacts are prone to wear out.
This schematic employs TRIACS, and a special optoTriac offers the insulation a TRIAC alone can't offer. Without the optoTRIAC, Nutchip's power and signal line would be connected to live mains! Caution is required as well when building this circuit, as the parts contained in the rightmost box (marked with DANGER!) are all at dangerourus (even lethal) live mains potentials.
The circuit works as follows: a Nutchip output drives optoTRIAC's internal LED. This in turn makes optoTRIAC's internal TRIAC into conduction, driving as a consequence the external power TRIAC which is connected through its gate (G) pin. The power triac is in series with the lamp.
TRIACS require exclusively AC powered loads. You can use it at lower voltages than mains 220V , e.g. 12 or 24Vac as used for small halogen bulbs. The circuit is NOT suitable for inductive loads, as motors, transformers, neon lights, halogen lamp transformers.

A single darlington-type transistor is a simple and efficient way to switch a DC motor on/off according to Nutchip output. A TIP122 type can drive motors powered at up to 40 volts requiring less than 600mA, without heathsink.

The motor runs when the output is 1, and stops when the output is 0.

Note: the schematic symbol for a darlington transistor resembles a transitor pair. This schematics actually requires only one darlington transistor (see components details)

This circuit is not designed to be used alone. It is used as a basis to build more complex circuits described in the following sections:

• DC motors with electronic brake
• DC motors with forward/reverse control
• Stepper motors

These motor drives require one or more copies of this sub-circuit. Every sub-circuit is controlled by a distinct Nutchip output, and drives a distinc motor's wire.
As two copies of this circuit are required to build an H-bridge driver, this circuits is often referred to as half-H-bridge.

To reverse the rotation direction two of the above circuits are required, which build a complete H-bridge. The motor is connected to the two MOTOR outputs. Two Nutchip outputs are required to drive the H-bridge halves.

Stepper motors require 4 identical copies of the half bridge circuit previously detailed. Each circuit drives one of the 4 motor wires (steppers have two coils internally). Therefore, all four Nutchip outputs are required to drive steppers. Here is the output sequence for stepping them:

To reverse rotation, just use the same sequence reversed, that is from last row to the first.

Nutchip outputs can drive directly TTL gates and 5V-powered CMOS gates.

This example shows how to connect a Nutchip output to one input of an AND logic gate. If the logic gate is on an external board, the negative power pins (GND) must be joined.

This circuit drives walkman-type earphones/headphones from a Nutchip output. Note how the outer ring on the jack is kept disconnected. This arrangment makes phones connected in series, giving the impression of a sound centered between your ears! Nutchips can produce a range of noises. Shorter delays produce tones, truth table with slow delays make clicks and cracks.

WARNING: depending on your earphones, volume can be quite loud. Put the phones on only after ascertaining the volume does not harm your ears! Increase R1 value to reduce volume.

Want a high-power buzzer? This circuit turns your stereo in an mega-siren. It connects to the AUX input, alternaely it can be connected to TAPE, CD or TUNER inputs. Use an RCA patch cable (from HiFi shops) to connect the female RCA circuit (CN1) to the amplifier, and switch it in MONO mode (you can also build a two identical copies of the circuit for a stereo output).

WARNING: this circuit produces a high-level output and very-low frequency signals. Start keeping your volume to a very low level, increase it gradually. Excessive power when reproduce high power signals and very-low frequencies can damage your speakers or harm your ears.

A 7-segment display is made from 8 (!) LEDs. Each LED illuminates a distinct segment on the actual digit. Segments are convetionally referred to with a letters a,b,c,d,e,f,g, with the h referring to the decimal point. To reduce pin count, either all of the LED cathodes or anodes are joined into a single pin. This is what we mean when talking about "common cathode" and "common anode" displays.

Display's segments can be illuminated exactly in the same way as plain LEDs (that is, whit a digital output and a series resistor); however, the most common practice is to use specilized display drivers IC like the CD4511, as detailed in this project.

Conecting an LDR as shown in this circuit, the value on IN4 is read as either 0 or 1 depending on the amount of light it receives.
This circuit is fast, so if the light source includes neon lights, video monitors and similar sources producing intermittent energy, a smoothing capacitor (about 100nF) can be added in parallel with the LDR.

A trimmer/potentiometer sets the light level at with the photocell triggers. Any value from 1 kiloohm to 470kiloohm can be used in place of the 100 kiloohm shown here.

Cristal resonators typical precision is better than 1%. For short periods (up to 50 hours) this frequency error is not significant. But if you are going to make cyclic or very long-delay timers, the error can accumulate and become visible. Just consider how a clock accumulating a one-minute error every 100 minutes results in a three-days error over a year!

The same applies for an external 4MHz clock source.

If you decide not to include the programming interface on-board, we suggest you to at least leave a programming connector for the necessary signals. The connector can host a PC interface in case you need to reprogram or monitor the Nutchip. The female connector must be suitable for fitting a male pin-strip whith pins spaced 2.54 mm apart. A cheap conector can be made from a 4+4 dual-in-line IC socket, cut in two.

This is the simplest and cheaper among the programming interfaces. It works with almost every small-signal PNP and NPN transistor pair.

Connector CN2 is a 2.54mm pin-strip provided for plugging into programming connector.

Tip: Should you include the whole cuircuit to your actual board, we suggest you to add a 10 kilooohm resistor across Q1 base and GND, to keep in stable should the PC be disconnected.

more details

If you use exclusively the 2 transistor interface above, you can adopt a simplifiede cable connecting olny 3 wires: pin 2, pin 3, and pin 5.

This is an improved variant of the previous circuit. It performs better in case of short power drops or interruptions: in fact, the diode discharges the capacitor very quickly hould the power drop. When the power comes back, the diode does not conduct and the resistor operates the power-on delay allowing power to stabilize before firing the Nutchip.