Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Switches controlled by Microcontroller

Status
Not open for further replies.
C

conanhaha

Junior Member level 2
Joined
Dec 20, 2008
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,486
Hi all~
Want to ask that,
I want to construct a tester circuit with various configuration values, such as different resistor values, I need many switches to close and open to change the resistor values.
This need to be controlled by a micro-controller.
What kind of switches that can be controlled by micro-controller which micro-controller can send signal to close/open the switches to change all the connecting resistors value?
 

All electronic switches are characterized by R[on] resistance (impedance) ..
If you can allow for R[on]<100 you can go for very common IC such as the CD4066 (or equivalent) ..

Rgds,
IanP
 

Sorry that I am new to this switching and can't understand well.
What is R[on] and what its mean of <100, how to c the value?

I had upload a sample switching that i wish to have.
When 1st test, I wish to connect to R1, R4, R7.
When 2nd test, I wish to connect to R2, R5, R8.
When 3rd test, I wish to connect to R3, R6, R9.

All need to be controlled by micro-controller.
Is that possible i use only 3 switch that can on the example>
(R1, R4, R7),
(R2, R5, R8 ),
(R3, R6, R9)
each at the same time?
 

R[on] is the channel/contact resistance and in your case is has to be quite low as it might introduce error – compare 100ohm of R[on} for CD4066 and 1kohm resistor ..

In such an instance you may have to consider the use of reed relays – some of them are in DIL-housing – but what's important about them is that the contact resistance is very low i.e. negligible comparing with values of resistor that you have around the uA741 ..

Here are some details:
https://www.kronosrobotics.com/Anotes/Relays.pdf

Rgds,
IanP
 

IanP said:
...may have to consider the use of reed relays – some of them are in DIL-housing...IanP
Click to expand...
The smallest one comercially available is only ca. 5x 2x 2.5mm:)
Reeds are (relative) HIGH-SPEED Relays.(Switxh time ~1-3 msec) & relative good for high-speed signal qualities too.
K.
 

Thanks for your reply.
In my case I will use 10ohm, 100ohm, 2k, and further more to 5Mohm resistors in the example circuit that i post. (quite big range).
Which kind of relay suitable for this kind configuration?
So the used of relay need any extra configuration?
Do i need a lot numbers of relays?
I saw some of the example configuration using relay connect to ULN2003 only connect to micro-controller. Relay must do like that?
 

To control your circuit you will need 9 relays ..

If you select a microcontroller that can source/sink at least 20mA from it’s pin – and most of them can – you will be able to drive these miniature reed relays directly from the microcontroller pins .. but driving relays through transistors is a better idea .. see picture below ..

Rgds,
IanP
 

Hi,
Hier is a good reed relay source:
https://www.directindustry.com/tab/miniatur-reed-relays.html#seProd

I must correct me: The smallest reed at 5mm is only a proximity sensor!!!

In all case you can have lot of different types from ca. 8 mm typical miniatur reeds hase a length of ca. 10-11mm...
https://www.cotorelay.com/html/reed_relay_9800_series.htm

You see, for all switcher(contacts) you need a relay, they are typcally with doppel contacts constructed-some types have more too- but a reead is as small volumen, speedy switch with relative godd RF datas, for me the best candidat.
Remember pls: it need such power-dissipating heath!
Other (conentionell types) need such more energy, are slower, bigger, and dont have parr millions of switches:)
Coto`s product family is very similar es the attached one-maybe is not cheaper too...
K.
 

I suggest to use widely available standard reed relays, e.g. RM5.08 or RM3.81 SIL (single in line) form factor. You considered
ULN2003 as a driver. Although not required for the rather low reed relais coil current, it's a way to reduce the overall part count.
The relays are also available with 5V coils and a resistance of 250 to 1000 ohm. The low current versions can be driven
by an uC port or IO-externder (e.g. 74HC595) directly.
 

Hi~ Thanks again for all replies~
My lecturer mention that with my circuit the reed relay should be can straight away connect to micro-controller without passing through darlington.
Since I need a lot number of relays, is that any IC that build a few relays together that can be used to connect to micro-controller?
 

It is true that you can drive certain types of relays directly from pins but in the same time you have to be aware that these devices have power dissipation limitations .. see attached table (eg. PIC16F88) ..
As you can see, it can source/sing the total of 200mA, that means roughly 10 pins@20mA, but be careful with this straight mathematical calculation and take into account other factors such as the max power (in this case 1W) , ambient temperature, and so on ..
You don’t want to operate microcontroller at, say, 75degC, do you?

Rgds,
IanP
 

Hi,
It's best to operate the relays and external components through transistors or transistor arrays like ULN2003/ULN2803/CA3081, etc.
Like IanP said,
These will help keep the temperature of the PIC at a more reasonable range.
 

Hi~ Thanks again for all reply~
How to calculate to see that the uC will go to overheat condition?
Sorry that i not really understand the explanation.
I had gone through the 5.08mm external depth reed relay, and found a few series of reed relay like COTO 9000 series, HE700, HE3600, HE3300 and so on.
Which one will be better to use?
The relay quite costly because i need quite a number of them.
 

“COTO 9000 series, HE700, HE3600, HE3300 and so on ..”
Any of them should b OK for your application, so choose those that are the most cost-effective/small size .. for example, (see attached picture) I like that one as it is very small and can be ordered with diode suppressed coil ..
The 5V version (single contact) coil’s resistance is ~500ohms - it’s driving current is ~10mA, so it looks like they can be driven directly ..

You haven’t mentioned what the type of microcontroller that is going to be used, so I can’t advice you whether it will overheat or not ..
Simply multiply number of reed relays by 10mA, compare with the maximum current through Vdd/Vss pins and that should give you the whole picture ..

Rgds,
IanP
 

I think I will use AT89C51 ED2 as my micro-controller.
But I not yet get it cause less selling on market :)
If I get a relay that got diode suppression coil mean that i do not need to add the diode IN4148 like attach on picture above?
By the way, when connect to ULN2003/ULN2803, I do not need to add in the diode also?
 

conanhaha said:
If I get a relay that got diode suppression coil mean that i do not need to add the diode IN4148 like attach on picture above?
Click to expand...
That's right ..
conanhaha said:
By the way, when connect to ULN2003/ULN2803, I do not need to add in the diode also?
Click to expand...
With pin [K=9] connected to Vcc - that's right too ..
See attached cartoon ..

Rgds,
IanP
 

Hi~
I saw most of the application connect with 12V relay and ULN2003 pin 9 is connected with 12V supply.
In my case I am using 5V reed relay which is HE3621A0500, the pin 9 of ULN2009 should be connected with 5V?
 

If relays are hooked up to +5V – Vcc means exactly that ..
[9] --> +5V

Rgds,
IanP
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top