Morning all,
I've purchased an OLED for use with a PICAXE project (same project as a while ago with the avago mouse sensor). It's a cool little thing, only 52x36 and very small, but that is what I want.
OLED:
I received it yesterday and all was going swimmingly until I took a closer look than I previously had, at the 16v power requirement.
I'd been banking on using an LM2577, which again, I've already bought. My proposed power train was: 7.4v li-poly feeding one step down regulator for logic circuit (2.8v) and one step up regulator for the OLED "drive" (16v).
The problem is this line in the bigger datasheet which I'd overlooked:
CPC on the other hand offer free delivery on anything placed online. You order one SMD cap today, you pay £0.60, you get it tomorrow. You realise you needed two, you buy another - wonderful.
So the question is, can we come up with a 16v power supply that can be switched to a floating state by the PICAXE, using parts from CPC?
Options I've thought of so far:
As for the OLED itself. It's a great little module. Would have been £60.74 if I'd bought the prototype power supply board from mouser at the same time. I managed to get it working with spimode11e and have already got it displaying stuff. I'm having some difficulties with the SPI commands but I think this may be sorted with a more proper power supply. I'm pulling out the driver wire when necessary.
Thanks in advance!
David
I've purchased an OLED for use with a PICAXE project (same project as a while ago with the avago mouse sensor). It's a cool little thing, only 52x36 and very small, but that is what I want.
OLED:
I received it yesterday and all was going swimmingly until I took a closer look than I previously had, at the 16v power requirement.
I'd been banking on using an LM2577, which again, I've already bought. My proposed power train was: 7.4v li-poly feeding one step down regulator for logic circuit (2.8v) and one step up regulator for the OLED "drive" (16v).
The problem is this line in the bigger datasheet which I'd overlooked:
The manufacturers recommend using a "MAX8574EUT+T" regulator since it leaves the output floating when in shutdown mode. They even provide a prototyping circuit with it for about £8 which is a bit steep, but fair enough. But the delivery is friggin £12 from mouser! For something that'll probably only cost about £1 to send!The VCC [16v] must be float, when it is not active, to conform to the required power ON/OFF sequences. This can be achieved with a relay or true shut down charge pump.
CPC on the other hand offer free delivery on anything placed online. You order one SMD cap today, you pay £0.60, you get it tomorrow. You realise you needed two, you buy another - wonderful.
So the question is, can we come up with a 16v power supply that can be switched to a floating state by the PICAXE, using parts from CPC?
Options I've thought of so far:
- Relay, as suggested in datasheet, to switch my LM2577. Two issues with this: 1) space, it would need to be a pretty small relay as the circuits are fitting in very small spaces. There's room for surface mount components, but nothing too tall. 2) Doesn't seem like a very elegant solution. To meet the power-on requirements, it would need to be normally off, so the coil would need a constant current to keep it on when in use. The battery is small so this would wear it out quite quickly. To solve that, it would need to be bi-stable, which would require more driver transistors, another PICAXE pin (I think?) and probably a bigger relay. A relay also just kind-of seems like overkill for what is needed - surely there's a better solution?
- Any other true shutdown regulators? I've looked on CPC and there are a few step up switching regulators that offer shutdown, but none say how the output is treated during shutdown. Does anyone know of a switching regulator with true shutdown, like the MAX8574EUT+T, but that can be bought for less that £12 in UK?
- Can my LM2577 be switched off in any other way? Using an FET to drive it for example? This is where my lousy circuitry knowledge becomes obvious.
- Are there any other options?
As for the OLED itself. It's a great little module. Would have been £60.74 if I'd bought the prototype power supply board from mouser at the same time. I managed to get it working with spimode11e and have already got it displaying stuff. I'm having some difficulties with the SPI commands but I think this may be sorted with a more proper power supply. I'm pulling out the driver wire when necessary.
Thanks in advance!
David