Today a little tidbit I came across while developing one of my projects. I was looking for a simple way to mechanically disconnect microcontroller/ESP controlled lines, with a minimum of additional components. This is how I came across the very small V23100-V4 dual signal relays. Interestingly, the manufacturer explicitly emphasises in the documentation that the coil can be controlled directly by TTL signals, which is immediately appealing for projects with microcontrollers.
Consider the parameters from the datasheet:
- maximum contact current: up to 1 A
- maximum voltage: up to 200 V
- maximum switching power: 10 W
For such a small relay, these are quite reasonable values - especially when it comes to signal applications or small loads. The coil parameters are also interesting:
- coil resistance: ~500 Ω
- coil power: ~50 mW
This means that the control current is very low, which is precisely what makes direct control from the microcontroller output possible (at least in many cases). In practice, it is important to check how much current can be drawn from the GPIO. For example, for the PIC18F2550 it is 25 mA:
Assuming a supply voltage of 5 V, about 10 mA will flow through the ~500 Ω coil. Well under the limit. Just what about lower voltages? According to the datasheet note:
- closing voltage (operate): 3.5 V
- opening voltage (release): 0.75 V
These values suggest that the relay is designed with low-voltage logic in mind. However, an interesting question arises: in practice, will it also work at even lower voltages than the declared 3.5 V? There is often some design reserve in such components, so I thought I would give it a go with ESP. DIY projects have their own rules, it's not mass production, so you can afford to do more. So it's time for testing.
The whole thing has a standard DIP raster, so it fits on a contact board:
Leads - yes, there is already a protection diode inside in parallel to the coil, so you can't connect the coil in reverse either:
First test at 5 V - no surprise here rather, the whole thing works.
Second test - controlled from ESP32 at 3.3 V:
Here I've stretched the specification a bit, as the manufacturer announces the contacts close from 3.5 V rather than 3.3 V, but nevertheless the relay works too.
In summary , this was an example of a small relay that in practice turns out to be much more 'friendly' to microcontrollers than the datasheet note alone might suggest. Thanks to the very low coil power consumption, it can in many cases be controlled directly from the GPIO, without an additional transistor. Of course, in production applications it is better to stick to the manufacturer's specifications, but in DIY projects such a reserve of parameters can be very useful.
Undoubtedly this was a rather beginner's topic, but I hope it may have interested someone.
Have you used this type of relay in projects, and if so, for what?
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