Any chance someone can tell me what microcontroller is on these boards? I would like to check the datasheet for absolute maximum ratings. If not, it would be nice to know if the 20mA output stated is actually the absolute maximum, or just a safe value.
Reason being I want to switch a relay with this output. The relay has a coil power of 150mW (30mA at 5v) which is above the stated output at this pin. That said, I notice that 6 pin PIC have a rating of 25mA and ATtiny have a rating of 40mA, so I thought that just maybe this little thing could supply more than 20mA.
And before all the suggestions flood in about using a high powered board, I want to use a relay to provide a level of isolation and the ability to use a range of power sources and switching options. Also, I will be making quite a few of these, so using the one with a small MOSFET to switch the relay will add up in quantities.
It is a PIC (10F202) on the board. The rating of 25mA is an absolute maximum, and the pin will probably be quite far from 5V by the time you’re pulling that much current from it. You could give it a try, but I think you might have trouble consistently turning various relays on. If you are going to need at least a few hundred of these, we might be able to make a semi-custom version for you. Making a version with a relay has been on the back burner for a while, and if what you want could be general enough that we think it would be appealing to others, we could probably do it without any extra engineering charges.
Hi Jan,
Thanks for that info, I think I’d be pushing it with that rating, and adding a bit of in-rush current when switching too. I tried a reed relay with a lower coil power, but it was not very reliable so I was hoping to use a subminiature relay.
I think my idea of “quite a few” is a bit different to yours (understandably). Especially in the short term, it will be a lot less. I also already have a few of the digital out switches, so that was another reason to use them.
If you were making one with a relay, I would have expected you to use basically the design with the small MOSFET and switch the relay with that, is that what you had in mind? Unless you could get a cheaper and still small, lower powered transistor in its place. If you were planning on a different approach, I’d like to hear it, I might be able to add some external circuit to drive the relay myself.
For my next order though, I think I will just use the switch with small MOSFET unless there is a better idea out there, or you decide to make one with a relay.
Yes, the non-relay portion would basically be like the unit with the small MOSFET. We might change the MOSFET, but there is not much to save since I think the MOSFET is only about 10 cents. The main thing that has kept us from going ahead with it is some kind of conviction that a particular relay is the one to use. With the MOSFET version, people can use a wide variety of relays. Do you have a particular relay you like?
I had a feeling that would be the case. And since I could solder many different relays directly into the switch with the small MOSFET, it’s not really an issue.
I think you brought up the important point that there are too many relays to chose from. The benefit of the MOSFET version is that you can use almost any dc relay and chose one for a specific application. It seems that the majority of your customers have some experience with electronics and soldering etc, so even just a mention that the MOSFET version would work well with a dc relay of their choice would be enough.
Just to answer your question, I have some subminiature 5vdc DPDT relays that I was planning to use(the coil pins fit directly onto the board output, so I can just solder wires onto the contact pins). They had the lowest coil power I could find, but they are only rated at 1A so they are not practical for many applications. In future since I will be using the MOSFET version switch, I would likely get relays with a higher current rating. I will be using these for different applications, so I think there will be a few different relays used along the way. Also, weight and size are considerations, so for each application I will consider how many poles are required and if double throw is required or not.
Thanks for your help, it’s good to know we can get more product info whever it’s required.
