# Wake up a Electron when powered by USB, not the lipo **URL:** \ **Category:** Troubleshooting\ **Created:** [February 5, 2019, 12:13am UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542 "2019-02-05T00:13:48Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![steeves](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/steeves/32/13652_2.png) [@steeves](https://community.particle.io/u/steeves)\ **Post date:** [February 5, 2019, 12:13am UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/1 "2019-02-05T00:13:48Z")
Hi My goal is using the Asset Tracking Electron, I want to put the Electron in Sleep mode when USB is not charging and wake up when USB is charging. Asset will be placed in a car and start tracking when the power come from the USB. In the Electron documentation, where is the section about this feature to detect when the Electron is powered by the USB not the battery ? ---
**Author:** ![ScruffR](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/scruffr/32/6952_2.png) [@ScruffR](https://community.particle.io/u/ScruffR)\ **Post date:** [February 5, 2019, 7:05am UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/2 "2019-02-05T07:05:00Z")
Since the Vin pin is not powered from the LiPo you can use that pin as a `RISING` edge wake pin. This would be the answer to your topic title, but whan you say ... > [@steeves](#): > > I want to put the Electron in Sleep mode when USB is not charging and wake up when USB is charging. ... this will only tell whether 5V is coming from USB, it doesn't tell anything about whether or not the LiPo gets charged or not (e.g. when fullly charged already). ---
**Author:** ![steeves](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/steeves/32/13652_2.png) [@steeves](https://community.particle.io/u/steeves)\ **Post date:** [February 5, 2019, 3:45pm UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/3 "2019-02-05T15:45:18Z")
Hi @ScruffR I don’t need to know if USB is charging, only if 5V is coming is fine for my use case. Do you have a example about best case to use `RISING` ? ---
**Author:** ![justicefreed\_amper](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/justicefreed_amper/32/16477_2.png) [@justicefreed\_amper](https://community.particle.io/u/justicefreed_amper)\ **Post date:** [February 5, 2019, 3:52pm UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/4 "2019-02-05T15:52:32Z")
Connect VIN to WKP pin with a 2.2k resistor in-between. Add a 3.3k resistor to ground on the WKP pin. Make sure pull-up/pull-down resistors for the WKP pin are disabled / don’t enable them in firmware. This converts 5V to ~3.3V using a resistive voltage divider network. When VIN goes from 0V to 5V because of 5V via the usb, this creates a transition from 0V to ~3.3V on the WKP pin which the processor will listen to to wake it up from sleep. You could then measure voltage by using WKP as an ADC pin (A7) periodically to determine when to go back to sleep. Test it to make sure those values work for you. Keep in mind tolerances to make sure the range of voltage outputs meets your requirements. ---
**Author:** ![ScruffR](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/scruffr/32/6952_2.png) [@ScruffR](https://community.particle.io/u/ScruffR)\ **Post date:** [February 5, 2019, 8:05pm UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/5 "2019-02-05T20:05:41Z")
Sure, extra precautions are nothing to appologise for but if you are after a minimal approach with pragmatic risk assessment the voltage dividers are not a must have. Some background > [@justicefreed\_amper](#): > > Make sure pull-up/pull-down resistors for the WKP pin are disabled / don’t enable them in firmware. This is difficult to achieve since `System.sleep()` will apply the respective pull-resistors depending on the trigger edge. So if you don't want an internal pull to be applied you'd need to trigger for CHANGE. Deep sleep always has uses the internal pull-down. A related comment/proposal exists in a pending firmware issue [https://github.com/particle-iot/device-os/issues/1149#issuecomment-257079898](https://github.com/particle-iot/device-os/issues/1149#issuecomment-257079898) However, as long you are _ **not** _ using A3 or A6 (aka DAC) as wake pin, you don't need a voltage divider as all pins (apart from the two) on the Photon/Electron are 5V tolerant (for a short time even with attached internal resistors). If the internal pull-resistors are _only_ attached for the sleep periode and after applying 5V the device immediately wakes and reverts to `pinMode(pin, INPUT)` - either by having had it assigned before Stop Mode sleep or by default after deep sleep - you should be good. > [@justicefreed\_amper](#): > > You could then measure voltage by using WKP as an ADC pin (A7) periodically to determine when to go back to sleep. When opting against the voltage divider make sure you _ **don't** _ `analogRead()` that pin but rather use `digitalRead()` which will again accept 5V and rid you of the need for a voltage divider. > [@steeves](#): > > Do you have a example about best case to use RISING ? Sure ```cpp // either System.sleep(SLEEP_MODE_DEEP, 3600); // deep sleep for 1h or till RISING edge detected on WKP // or System.sleep(D1, RISING, 3600); // Stop mode sleep for 1h or till D1 goes HIGH // for that version make sure you either don't set pinMode() or // exlplicitly set it to pinMode(D1, INPUT) any time before sleeping // or immediately after the System.sleep() call where the code will follow // on after wake ``` ---
**Author:** ![steeves](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/steeves/32/13652_2.png) [@steeves](https://community.particle.io/u/steeves)\ **Post date:** [February 5, 2019, 9:21pm UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/6 "2019-02-05T21:21:23Z")
Which pin can be use to validate if USB is connected with 5V is the A7 ? Like that `System.sleep(A7, RISING, 3600);` ---
**Author:** ![ScruffR](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/scruffr/32/6952_2.png) [@ScruffR](https://community.particle.io/u/ScruffR)\ **Post date:** [February 5, 2019, 10:17pm UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/7 "2019-02-05T22:17:25Z")
A7 is WKP and can be used with either sleep mode. ---
**Author:** ![steeves](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/steeves/32/13652_2.png) [@steeves](https://community.particle.io/u/steeves)\ **Post date:** [February 6, 2019, 1:16am UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/8 "2019-02-06T01:16:35Z")
Thanks @ScruffR I’ll test it and let you know ---
**Author:** ![steeves](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/steeves/32/13652_2.png) [@steeves](https://community.particle.io/u/steeves)\ **Post date:** [February 7, 2019, 11:53pm UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/9 "2019-02-07T23:53:15Z")
Hi @ScruffR I try to test just like this code. I don’t have installed 2.2k resistance between VIN and WKP and 3.3k from WKP to ground. Do I need to make this setup to run my code ? Actually is not working. Note : I don’t test sleep for now, just try using attachInterrupt. When done, I’ll use the System.sleep( Thanks ```auto void hello(void); void setup() { pinMode(A7, INPUT_PULLDOWN); attachInterrupt(A7, hello, RISING); } void loop() { } void hello() { Particle.publish("I am blink", PRIVATE); } ``` ---
**Author:** ![ScruffR](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/scruffr/32/6952_2.png) [@ScruffR](https://community.particle.io/u/ScruffR)\ **Post date:** [February 8, 2019, 6:21am UTC](https://community.particle.io/t/wake-up-a-electron-when-powered-by-usb-not-the-lipo/47542/10 "2019-02-08T06:21:48Z")
You cannot use `Particle.publish()` from within an ISR. Try this instead ```cpp void hello(void); void setup() { pinMode(D7, OUTPUT); pinMode(A7, INPUT); attachInterrupt(A7, hello, RISING); } void hello() { static uint32_t ms = 0; if (millis() - ms < 200) return; // simple 200ms debounce ms = millis(); digitalWrite(D7, !digitalRead(D7)); // toggle D7 LED } ``` For this you _ **do** _ need an external pull-down e.g. 10k (should be possible to go higher tho') on A7 and a connection between Vin and A7 (for safety I'd add a 470Ohm resistor to limit current in case of inadvertent OUTPUT LOW). The external pull-down is required since this condition doesn't apply to your test setup > [@ScruffR](#): > > If the internal pull-resistors are only attached for the sleep periode and after applying 5V the device immediately wakes and reverts to pinMode(pin, INPUT) [...] you should be good. So with a test code like this, where you _need_ and external pull-down anyway, the voltage divider is the better approach after all - although I'd maybe increase the values to reduce current while USB powered (e.g. 10k + 6k8).