# How to control AC device using microcontroller

#### Parth786

Joined Jun 19, 2017
642
Hi
How to control AC device using 8051. For example I have two devices. Device 1 work on 240 AC and Device 2 work on 30 AC. First I want to control Device 2 using 8051 MCU. I am looking information about driver module. I did google search and I found that we will use relay and other electronic components but I don't have idea how to do it. whats I need to make driver module to operate 30 AC device ?

#### ScottWang

Joined Aug 23, 2012
7,326
Device 2 work on 30 AC
30Vac and current ?
Use relay or low Rds and high current MOSFET to control device2 30Vac/I.

#### Parth786

Joined Jun 19, 2017
642
30Vac and current ?
Use relay or low Rds and high current MOSFET to control device2 30Vac/I.
I don't have specific device in mind. I just wanted to learn how do we control AC device using MCU. Once I get Idea I will think about specific device

lets assume following specification

Specification for AC device
Voltage = 30 V AC
Current = 4 Amp AC
There are many relay and mosfet available in market. so How to pick right one for device 2 ?

#### Picbuster

Joined Dec 2, 2013
1,041
Hi
How to control AC device using 8051. For example I have two devices. Device 1 work on 240 AC and Device 2 work on 30 AC. First I want to control Device 2 using 8051 MCU. I am looking information about driver module. I did google search and I found that we will use relay and other electronic components but I don't have idea how to do it. whats I need to make driver module to operate 30 AC device ?
View attachment 136083
Use a frequency inverter price 120$approx. ( eq high end Hitachi but cheaper brands available see internet) input 4- 20mA or 0-5V produce 0-100% speed left/right 0-5V rush in current control, slow start all available. Extreme simple to couple it with you MCU. no way you can build one cheaper. Picbuster Thread Starter #### Parth786 Joined Jun 19, 2017 642 Use a frequency inverter price 120$ approx. ( eq high end Hitachi but cheaper brands available see internet)
input 4- 20mA or 0-5V produce 0-100% speed left/right 0-5V
rush in current control, slow start all available.

Extreme simple to couple it with you MCU.
no way you can build one cheaper.
Picbuster
Thanks for your offer But I don't want to buy it. I want to learn how do we make circuit. and how do we select components for circuit?

#### ScottWang

Joined Aug 23, 2012
7,326
Use relay is more easier for simple AC control, but if you want to learn how to using uC signal to control low AC device (as 30 Vac) with N MOSFET then you can see -- Using two Mosfets for AC.

If you want to make the circuit simply then choosing the Vgs has logic level as 4.5V.

#### Parth786

Joined Jun 19, 2017
642
Use relay is more easier for simple AC control, but if you want to learn how to using uC signal to control low AC device (as 30 Vac) with N MOSFET then you can see -- Using two Mosfets for AC.

If you want to make the circuit simply then choosing the Vgs has logic level as 4.5V.
I want to use Relay. I am familiar with 5v dc and 12 v Dc relay. I want to learn how to using uC signal to control AC device

8051 --- Relay --- AC device (30 v AC)

I don't think that one relay is enough to drive 30 AC device. I think I need to add additional circuitry. correct me if I am wrong. I have never design circuit for AC device. So I don't have any idea. I have only read that we can do it using relay and mosfet. so I just want make circuit. Please help me to build circuit.

#### MrChips

Joined Oct 2, 2009
28,114
You don't need a circuit. A single device will do it. It is called a Solid State Relay or SSR.

https://www.sparkfun.com/products/13015

• logic level low voltage input 3-32VDC
• controls 24 - 380VAC @ 40A (DC voltage SSR also available)
• zero-crossing switching
• optical isolation

#### simozz

Joined Jul 23, 2017
125
I don't have specific device in mind. I just wanted to learn how do we control AC device using MCU. Once I get Idea I will think about specific device.
So it's impossible to give you a solution if you don't know what you want to do..
If you just want to turn on and off a 30 Vac load the solution could be a relay driven with a transistor.
If you want to modulate the load power using PWM, you will not use a relay of course.
The solution depends on what you want/have to do.
Also, forgive relays if you need fast switching..
simozz

#### ScottWang

Joined Aug 23, 2012
7,326
The Ic of bjt will be limited by R1 with hFE=10, and it is also limited the current of relay coil.
The bjt I would prefer the 2SC1384(1A).

You can find the contact current of relay is 10A or more, and the contact voltage is 36 Vdc or 45 Vac or more, if you could find a 5V relay have the similar contact voltage/current then it is ok, the Vgs = 4.5V logic level of N MOSFET is better.

#### Parth786

Joined Jun 19, 2017
642
You don't need a circuit. A single device will do it. It is called a Solid State Relay or SSR.
I understood. MCU will control Relay and Relay will control ac device. Does it means relay take 5 dc signal from mcu and supply 240 ac signal 240 ac signal to light bulb ?

#### MrChips

Joined Oct 2, 2009
28,114
No. Does that make any sense? Think about it.

380V x 40A = 15kW

Where are you going to get that amount of power?

#### Parth786

Joined Jun 19, 2017
642
No. Does that make any sense? Think about it.

380V x 40A = 15kW

Where are you going to get that amount of power?
No That can not possible. Relay can enable or disable ac device. I need to supply 240 AC to light bulb. Three pins of relay will connect to MCU and Two pins of Relay will connect to light bulb.

Last edited:

#### MrChips

Joined Oct 2, 2009
28,114
No.

There are only four pins to the relay.

3 - 4 are connected to your microcontroller (8051)
1 - 2 are your switched output - you supply your own power to the light bulb.

1 - 240VAC LINE
2 - light bulb
(make your own connection from light bulb back to NEUTRAL)

3 - +5V MCU supply voltage
4 - MCU open-collector output (sink to GND).