# Zymkey 4i plus 20x2 LCD I2C Display problem **URL:** \ **Category:** ZYMKEY4\ **Created:** [April 6, 2019, 8:12pm UTC](https://community.zymbit.com/t/zymkey-4i-plus-20x2-lcd-i2c-display-problem/488 "2019-04-06T20:12:20Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![nonoti](https://avatars.discourse-cdn.com/v4/letter/n/8baadc/32.png) [@nonoti](https://community.zymbit.com/u/nonoti)\ **Post date:** [April 6, 2019, 8:12pm UTC](https://community.zymbit.com/t/zymkey-4i-plus-20x2-lcd-i2c-display-problem/488/1 "2019-04-06T20:12:20Z")
How many milliamps does the Zymkey draw? I’m having a problem whereby I have an LCD 20x2 matrix screen in i2c mode connected above the Zymkey (same pins with an extender\*). When the Zymkey is initialised and running, the LCD screen seems to very dim and unclear. But if I display something on the LCD display and do an OS shutdown and the Zymkey is de-activated the LCD screen is suddenly sharp and bright again? \*LCD is connected to pins 2 & 6 for power, and 3 & 5 for data. The Pi is powered through its USB power supply with a 5V 2.5A supply. ---
**Author:** ![Phil\_S\_Zymbit\_1](https://avatars.discourse-cdn.com/v4/letter/p/45deac/32.png) [@Phil\_S\_Zymbit\_1](https://community.zymbit.com/u/Phil_S_Zymbit_1)\ **Post date:** [April 6, 2019, 8:39pm UTC](https://community.zymbit.com/t/zymkey-4i-plus-20x2-lcd-i2c-display-problem/488/2 "2019-04-06T20:39:19Z")
Zymkey draws only a few milliamps when powered, and a few microamps when running of battery. So its definitely not hogging power from your supply/LCD. Have you checked that your LCD is not conflicting on the I2C bus address (by default, Zymkey uses slave address 0x30), or GPIO4 (zymkey needs exclusive access to this pin) ---
**Author:** ![nonoti](https://avatars.discourse-cdn.com/v4/letter/n/8baadc/32.png) [@nonoti](https://community.zymbit.com/u/nonoti)\ **Post date:** [April 6, 2019, 9:43pm UTC](https://community.zymbit.com/t/zymkey-4i-plus-20x2-lcd-i2c-display-problem/488/3 "2019-04-06T21:43:04Z")
Hi Phil, Thanks for the reply. I’ve tried another power source, only 2.4A but now the problem is NOT showing itself. So it must be power related I would guess. I’ll have to give some more attention to the power supplies i’m using. The 2.5A one is a wallplug transformer connected to a barrel connector (DC plug) which is then spliced into a micr USB to plug into the Pi. The 2.4A one is a universal cellphone charger pushing out 5V and 2.4A. Its odd that this one works better but maybe something is not working nicely in the use of the DC plug and barrel connector. ---
**Author:** ![Phil\_S\_Zymbit\_1](https://avatars.discourse-cdn.com/v4/letter/p/45deac/32.png) [@Phil\_S\_Zymbit\_1](https://community.zymbit.com/u/Phil_S_Zymbit_1)\ **Post date:** [April 7, 2019, 12:41am UTC](https://community.zymbit.com/t/zymkey-4i-plus-20x2-lcd-i2c-display-problem/488/4 "2019-04-07T00:41:47Z")
Good to hear you resolved you problem ! FYI, the Quality of power supply matters with RPi and with Zymkey. The following explains why: > [@Power Quality - How it Impacts Software & System Reliability](https://community.zymbit.com/t/power-quality-how-it-impacts-software-system-reliability/243): > > Applicable Products The information included in this post applies to all Zymbit security modules. Power & Security Poor power quality can result in unstable and potentially insecure operation of your single board computer (SBC), depending upon it’s design, operating conditions and related system and power components. In this post we will outline the important factors of power quality management and explain how Zymkey manages the security of your device when power quality is poor. Power Qualit…